Agilent E3610A - Shorted transformer?

[andy3055]

Can you post a picture of your transformer?

It is difficult, of course! But at least, like I said, you can see if it is just shorted close to the "top end" of the primary winding and fix it. Winding back the secondary windings are not that hard if you keep a count of the number of turns in each segment. You may be able to use the same wire also if you are careful. Use some cotton gloves to keep the oil from your hands away. Once it is done (if you decide to do so) put the thing in a metal container with a high wattage bulb to "bake" it. Good if you can re-varnish it. You may not find the varnish though in your area. Something like this: https://www.ebay.com/itm/331529483474?epid=9011367709&hash=item4d30b274d2:g:DOMAAOSwqu9VLBIl

Like mentioned by JW above, the easier thing to do is to find another transformer that will have the same outputs (very unlikely though) or look for a guy who does this for a living. It should not cost that much.

[augustol]

Can you post a picture of your transformer?

It is difficult, of course! But at least, like I said, you can see if it is just shorted close to the "top end" of the primary winding and fix it. Winding back the secondary windings are not that hard if you keep a count of the number of turns in each segment. You may be able to use the same wire also if you are careful. Use some cotton gloves to keep the oil from your hands away. Once it is done (if you decide to do so) put the thing in a metal container with a high wattage bulb to "bake" it. Good if you can re-varnish it. You may not find the varnish though in your area. Something like this: https://www.ebay.com/itm/331529483474?epid=9011367709&hash=item4d30b274d2:g:DOMAAOSwqu9VLBIl

Like mentioned by JW above, the easier thing to do is to find another transformer that will have the same outputs (very unlikely though) or look for a guy who does this for a living. It should not cost that much.

This weekend I will remove it from the board and post some pictures here. For now, I'm assessing costs for rewinding. I found some companies that rewind transformer, but by the looks of it, they only work with huge power transformers. I sent those companies an email, let's see if one of them will do it.

I'm actually up to rewinding it myself but if I have to redo all the windings might be cheaper to get two or three transformers to replace this one. And I would probably have to put the outside of the power supply, it will be very ugly, but functional. Since covid the prices of copper wire skyrocketed here, let's see how this goes. But if I'm able to reuse most of the wire, it might be a good choice.

[andy3055]

Big companies will not do this. Too much trouble for them. Find a small motor winding place. If you have to wind the primary, it is a lot of work as the wire will be too small to handle.

[pqass]

I think you can replace the custom factory transformer with a standard 24VAC center-tapped toroidal tansformer plus adding two more secondary windings (~9VAC, ~30VAC CT).

https://www.digikey.ca/en/products/detail/hammond-manufacturing/1182M12/4809336

The service manual says that TP2-to-TP4 (the transformer's main secondary) is 25VAC +/- 10%  (note 6 on page A-9)
The 9VAC custom winding supports +5VDC for the front panel which is a pair of standard 7107 ADCs + 7-seg displays. 
The 30VAC winding is center-tapped to support up to +/-12VDC rails for the opamps etc. 
Both are regulated with 78XX/79XX series regulators; up to 1A but likely much less is used.

The E3610A has an input power rating of 70W.  So I found the above 80VA transformer that has 89mm diameter and 38mm height.  I own a E3611A and the distance from the top of the heatsink where the factory transformer sits to just under the case is about 45mm. Just find a 1mm thick aluminum plate to rest on the old transformer bolt holes and mount the toroidal transformer on top of that.

You probably could also get away with the 1182L12 at 50VA (giving 24V@2A or 12V@4A) but it's only marginally cheaper. I think this is a simple and elegant solution fitting for a premium power supply.

[augustol]

I think you can replace the custom factory transformer with a standard 24VAC center-tapped toroidal tansformer plus adding two more secondary windings (~9VAC, ~30VAC CT).

https://www.digikey.ca/en/products/detail/hammond-manufacturing/1182M12/4809336

The service manual says that TP2-to-TP4 (the transformer's main secondary) is 25VAC +/- 10%  (note 6 on page A-9)
The 9VAC custom winding supports +5VDC for the front panel which is a pair of standard 7107 ADCs + 7-seg displays. 
The 30VAC winding is center-tapped to support up to +/-12VDC rails for the opamps etc. 
Both are regulated with 78XX/79XX series regulators; up to 1A but likely much less is used.

The E3610A has an input power rating of 70W.  So I found the above 80VA transformer that has 89mm diameter and 38mm height.  I own a E3611A and the distance from the top of the heatsink where the factory transformer sits to just under the case is about 45mm. Just find a 1mm thick aluminum plate to rest on the old transformer bolt holes and mount the toroidal transformer on top of that.

You probably could also get away with the 1182L12 at 50VA (giving 24V@2A or 12V@4A) but it's only marginally cheaper. I think this is an simple and elegant solution fitting for a premium power supply.

Note: I just found a supplier that can make custom transformers in low quantity. I'm excited! I think this will work!

Now, I'm still confused about something: note 6 on page A-9 says the voltage between TP2 and TP4 is 25V +/-10% in low current range. Will this be different in high current mode?

Plus, it does look a lot like a center tapped transformer, am I being dumb assuming this is a 50V center tapped? But the drawing the center tap is bit out of center. Is it possible they are different voltages or am I just being paranoid? Or they are completely different windings?

EDIT

Sorry for the tons of silly basic questions. I'm learning and transformers are not something I've dig in deeper yet. Also, thanks to everyone, I'm learning a lot here. <3

[pqass]

Note: I just found a supplier that can make custom transformers in low quantity. I'm excited! I think this will work!

Now, I'm still confused about something: note 6 on page A-9 says the voltage between TP2 and TP4 is 25V +/-10% in low current range. Will this be different in high current mode?

The note is basically telling you the max. winding voltage of the secondary but, come to think about it, I assumed that the center-tapped point is at half that; 12VAC.   I may be wrong.  Why don't you measure the resistance of each half of the seconary to confirm that it is, in fact, at the half-way point. It could be a 14VAC/10VAC or other odd split.

In high-current mode, S2A switch only takes current from half (?) the secondary so that means it must sustain the full rated output of the power supply of 3A.  So, I misspoke about using the  50VA (1182L12) transformer as its rating requires both secondaries to be in parallel to sustain 4A (however, 1182M12 can sustain 3.3A on just one half).

Plus, it does look a lot like a center tapped transformer, am I being dumb assuming this is a 50V center tapped? But the drawing the center tap is bit out of center. Is it possible they are different voltages or am I just being paranoid? Or they are completely different windings?

EDIT

Sorry for the tons of silly basic questions. I'm learning and transformers are not something I've dig in deeper yet. Also, thanks to everyone, I'm learning a lot here. <3

It may look a bit off but I wouldn't trust the visual.  If each half is different it should say so somewhere.
In the absence of that, I'd confirm by actually checking both winding resistances.

It's NOT a 50VAC CT (or 25VAC-0-25VAC)  for sure! 
The reason that it's using half the secondary to produce a max. 8V output is so that it only has to burn 4VAC vs. 12VAC+4VAC to get 8VDC out (@3A; 12W vs 48W in the output transistors).

FYI: I measure 51VDC between TP2 and TP4 on my E3611A which makes sense since my supply can go to 40VDC output. And is consistent with note 6: "E3611A 47V +/- 10%"

[pqass]

So I had a poke in my E3611A and measured the pins directly off of the transformer.  This is what I see between the following pins (the square pad is pin 1, values shown are RMS):

• pin 1 - 2: 8VAC
• pin 3 - 4: 15VAC
• pin 4 - 5: 15VAC
• pin 3 - 5: 30VAC
• pin 6 - 7: 38VAC
• pin 6 - 8: 25VAC
• pin 7 - 8: 12VAC

Although I have a E3611A vs your E3610A we share the same design and only differ in a subset of component values.

• pin 1 - 2 is the winding for the front-panel.
• pin 3 - 4 - 5 is the center-tapped winding for the opamps (pin 4 is the center).
• pin 6 - 8 - 7 is the center-tapped main winding being controlled to the output posts (pin 8 is the "center").  But pin 8 is NOT a typical center where half the voltage is above and half below  This one is 25VAC below and 12VAC above; 2/3rd to 1/3rd ratio.  This makes sense since my PS output range is 20VDC and 35VDC.  Your PS's range is 8VDC and 15VDC which is closer to 50/50. So I would expect your transformer be wound differently than mine for this winding.  Also, I found an ERROR IN THE SCHEMATIC; pins 7 and 8 of the transformer are swapped! I've confirmed it by following the trace on the board.
  

[augustol]

So I had a poke in my E3611A and measured the pins directly off of the transformer.  This is what I see between the following pins (the square pad is pin 1, values shown are RMS):

• pin 1 - 2: 8VAC
• pin 3 - 4: 15VAC
• pin 4 - 5: 15VAC
• pin 3 - 5: 30VAC
• pin 6 - 7: 38VAC
• pin 6 - 8: 25VAC
• pin 7 - 8: 12VAC

Although I have a E3611A vs your E3610A we share the same design and only differ in a subset of component values.

• pin 1 - 2 is the winding for the front-panel.
• pin 3 - 4 - 5 is the center-tapped winding for the opamps (pin 4 is the center).
• pin 6 - 8 - 7 is the center-tapped main winding being controlled to the output posts (pin 8 is the "center").  But pin 8 is NOT a typical center where half the voltage is above and half below  This one is 25VAC below and 12VAC above; 2/3rd to 1/3rd ratio.  This makes sense since my PS output range is 20VDC and 35VDC.  Your PS's range is 8VDC and 15VDC which is closer to 50/50. So I would expect your transformer be wound differently than mine for this winding.  Also, I found an ERROR IN THE SCHEMATIC; pins 7 and 8 of the transformer are swapped! I've confirmed it by following the trace on the board.
  

Have you noticed that the note 6 on page A-9 might also be incorrect? You measured a total 38V on your E3611A, right? The note says it should be 47V. It caught my attention because because I was looking at the schematic and remembering the thing you said about the 1/3 2/3 ration between them. I also remembered that the low current should be 25V in my unit according to the notes. If I apply 25V as a 2/3 ratio, the total voltage should be 38V.

I actually didn't remember your measurements so I came back here to check it because I though it was way to high supplying 38V to output 15V max. Also, the other taps give more voltage to the regulator but not that much. 8~9V become 5V, 15V becomes +/-12V. Getting 38V to supply 15V sounded odd to me.

I'll later check if pins 7 and 8 are also swapped in my unit. But I guess they'll be.

[augustol]

Can you post a picture of your transformer?

It is difficult, of course! But at least, like I said, you can see if it is just shorted close to the "top end" of the primary winding and fix it. Winding back the secondary windings are not that hard if you keep a count of the number of turns in each segment. You may be able to use the same wire also if you are careful. Use some cotton gloves to keep the oil from your hands away. Once it is done (if you decide to do so) put the thing in a metal container with a high wattage bulb to "bake" it. Good if you can re-varnish it. You may not find the varnish though in your area. Something like this: https://www.ebay.com/itm/331529483474?epid=9011367709&hash=item4d30b274d2:g:DOMAAOSwqu9VLBIl

Like mentioned by JW above, the easier thing to do is to find another transformer that will have the same outputs (very unlikely though) or look for a guy who does this for a living. It should not cost that much.

Here are the pictures:

[augustol]

Ok, so... Updates:

I removed the transformer and did some measurements in DC Ohms.

Primary: 2.5 ohms
Pins 1-2: 1.2 ohms
Pins 3-5: 8.3 ohms
Pins 6-8: 0.8 ohms

A note here: my multimeter is not acurrate at all in low ohms (under 20, maybe 50). If I short the leads, for example I measure 0.8 ohms.

I guess is no the primary that's shorted after all. It's the main output.

I measured for ohms between the plus and minus of the (removed) bridge rectifier in the main output, I got no reading in any range. I tried continuity and all I got was a charging cap. I guess it's a sign it's not shorted. I will investigate the board further, though.

[pqass]

So I had a poke in my E3611A and measured the pins directly off of the transformer.  This is what I see between the following pins (the square pad is pin 1, values shown are RMS):

• pin 1 - 2: 8VAC
• pin 3 - 4: 15VAC
• pin 4 - 5: 15VAC
• pin 3 - 5: 30VAC
• pin 6 - 7: 38VAC
• pin 6 - 8: 25VAC
• pin 7 - 8: 12VAC

Although I have a E3611A vs your E3610A we share the same design and only differ in a subset of component values.

• pin 1 - 2 is the winding for the front-panel.
• pin 3 - 4 - 5 is the center-tapped winding for the opamps (pin 4 is the center).
• pin 6 - 8 - 7 is the center-tapped main winding being controlled to the output posts (pin 8 is the "center").  But pin 8 is NOT a typical center where half the voltage is above and half below  This one is 25VAC below and 12VAC above; 2/3rd to 1/3rd ratio.  This makes sense since my PS output range is 20VDC and 35VDC.  Your PS's range is 8VDC and 15VDC which is closer to 50/50. So I would expect your transformer be wound differently than mine for this winding.  Also, I found an ERROR IN THE SCHEMATIC; pins 7 and 8 of the transformer are swapped! I've confirmed it by following the trace on the board.
  

Have you noticed that the note 6 on page A-9 might also be incorrect? You measured a total 38V on your E3611A, right? The note says it should be 47V. It caught my attention because because I was looking at the schematic and remembering the thing you said about the 1/3 2/3 ration between them. I also remembered that the low current should be 25V in my unit according to the notes. If I apply 25V as a 2/3 ratio, the total voltage should be 38V.

Trap for young players there...   Notice note 6 says between TP2 and TP4. Well those points are AFTER the bridge and the main bulk cap C2, and are in DC!  Since I didn't have a load attached at the output posts on the front panel (and with range button on low - pushed in) then the voltage at the test points will basically be the peak of the wave.  I measured 38VAC (this is RMS) on the transformer pins 6-7, therefore the peak is 38*sqrt(2)=53VDC less 2 diode drops is 51VDC.  This is within 10% of 47VDC as per note 6 so I have no reason to doubt the values for the other PS models.

The reason note 6 says to put it in low mode is so that the S2A switch uses the full secondary and not (in my case) the 2/3rds position.

In your case, the E3610A, the low position is your whole secondary of 25VDC and my expectation of your transformer to be a true 50/50 split, so your high position should pick the center, therefore, should output 12.5VDC.   

I'm NOT saying all transformers will be 2/3rds - 1/3rd split like mine. These are are all custom transformers for each model so I assume the split would be according to the ratio of the hi/low voltages on the front panel label.

I actually didn't remember your measurements so I came back here to check it because I though it was way to high supplying 38V to output 15V max. Also, the other taps give more voltage to the regulator but not that much. 8~9V become 5V, 15V becomes +/-12V. Getting 38V to supply 15V sounded odd to me.

I'll later check if pins 7 and 8 are also swapped in my unit. But I guess they'll be.

Although my E3611A is labeled 0-20V (range button out) or 0-35V (range button in) my voltage dial can go 0-33V or 0-40V, with no load attached.  If the range button is on high (button out) the TP2-TP4 voltage sinks to 33VDC; this is used to guarantee 20VDC (not 15VDC as you said).  With a load attached, in hi-mode I can sustain 26V@1.5A (any higher voltage I go into CC mode) and in low-mode 40V@0.84A; this over the rating!

[pqass]

Ok, so... Updates:

I removed the transformer and did some measurements in DC Ohms.

Primary: 2.5 ohms
Pins 1-2: 1.2 ohms
Pins 3-5: 8.3 ohms
Pins 6-8: 0.8 ohms

A note here: my multimeter is not acurrate at all in low ohms (under 20, maybe 50). If I short the leads, for example I measure 0.8 ohms.

I guess is no the primary that's shorted after all. It's the main output.

I measured for ohms between the plus and minus of the (removed) bridge rectifier in the main output, I got no reading in any range. I tried continuity and all I got was a charging cap. I guess it's a sign it's not shorted. I will investigate the board further, though.

You'll have to lift one leg of C1 otherwise you'll just mess the readings.

If you could measure all three; between 6-7, 7-8, and 6-8 using croc/aligator clips (so hand pressure is removed from the readings) that would allow us to determine the ratio in the main center-tapped winding.   The actual low resistance value is not important; just that you did all three in the same manner.

My expectation is that pin 8 is the center-tapped, pin 6 is one side, and pin 7 is the other side of the secondary. Based on your E3610A being labeled as 8V (hi-mode) or 15V (low-mode), a ratio of approx. 50/50, I expect a 50/50 in each half of the secondary. So, I predict 6-8 should have the same resistance as 7-8, and 6-7 is twice that.

Let me know otherwise.

[augustol]

Trap for young players there...   Notice note 6 says between TP2 and TP4. Well those points are AFTER the bridge and the main bulk cap C2, and are in DC!  Since I didn't have a load attached at the output posts on the front panel (and with range button on low - pushed in) then the voltage at the test points will basically be the peak of the wave.  I measured 38VAC (this is RMS) on the transformer pins 6-7, therefore the peak is 38*sqrt(2)=53VDC less 2 diode drops is 51VDC.  This is within 10% of 47VDC as per note 6 so I have no reason to doubt the values for the other PS models.

Oh... haha Yeah, I should've taken that into consideration. I actually saw that when I was reading and identifying the points and etc, but I didn't really think through that. You are right.

You'll have to lift one leg of C1 otherwise you'll just mess the readings.

I did, actually. I was measuring the DC side. I was probably reading C2 which for now I do not intend to mess with. I did find a strange reading in CR3 though, the diode in the output which I supose is a reverse voltage protection. Not saying it's buned yet. I'll have to lift one of it's legs and measure again. Might just be because it's in circuit.

If you could measure all three; between 6-7, 7-8, and 6-8 using croc/aligator clips (so hand pressure is removed from the readings) that would allow us to determine the ratio in the main center-tapped winding.   The actual low resistance value is not important; just that you did all three in the same manner.

Ok, so I did the measurements again between all the taps with alligator clips, but not a big difference:

Primary: 2.2R
1-2: 1.2R
3-4: 4.5R
4-5: 4.4R
3-5: 8.1R
6-7: 0.8R
7-8: 0.8R
6-8: 0.8R

EDIT:

Like you said, it makes sense that in the E3610A should have symmetrical taps on the output part. Which makes the second tap 12.x volts. Which makes sense for delivering 8V.

[pqass]

...
The reason note 6 says to put it in low mode is so that the S2A switch uses the full secondary and not (in my case) the 2/3rds position.

In your case, the E3610A, the low position is your whole secondary of 25VDC and my expectation of your transformer to be a true 50/50 split, so your high position should pick the center, therefore, should output 12.5VDC.   

...

CORRECTION: Note 6 says to expect 25VDC on TP2-TP4 (E3610A) and we assume the peak of the wave when output is unloaded. Therefore, using my earlier math backwards, what's the AC volts (RMS)?    A: 25VDC/sqrt(2)=18VAC and the center-tapped is 9VAC (assumes 50/50 split; reasoning in my last message).

[pqass]

I did, actually. I was measuring the DC side. I was probably reading C2 which for now I do not intend to mess with. I did find a strange reading in CR3 though, the diode in the output which I supose is a reverse voltage protection. Not saying it's buned yet. I'll have to lift one of it's legs and measure again. Might just be because it's in circuit.

If you removed the bridge, you should be measuring across the AC ("~") pads with C1 leg lifted and the range switch in low-mode (pushed-in). That way you'll get the full secondary winding.

Ok, so I did the measurements again between all the taps with alligator clips, but not a big difference:

Primary: 2.2R
1-2: 1.2R
3-4: 4.5R
4-5: 4.4R
3-5: 8.1R
6-7: 0.8R
7-8: 0.8R
6-8: 0.8R

Those last three are a problem. 6-7 should be equal to the other two added together.
Given my last message (thinking now you have a 18VAC CT secondary) I don't think your meter can actually measure such a small winding.

[augustol]

I did, actually. I was measuring the DC side. I was probably reading C2 which for now I do not intend to mess with. I did find a strange reading in CR3 though, the diode in the output which I supose is a reverse voltage protection. Not saying it's buned yet. I'll have to lift one of it's legs and measure again. Might just be because it's in circuit.

If you removed the bridge, you should be measuring across the AC ("~") pads with C1 leg lifted and the range switch in low-mode (pushed-in). That way you'll get the full secondary winding.

Ok, so I did the measurements again between all the taps with alligator clips, but not a big difference:

Primary: 2.2R
1-2: 1.2R
3-4: 4.5R
4-5: 4.4R
3-5: 8.1R
6-7: 0.8R
7-8: 0.8R
6-8: 0.8R

Those last three are a problem. 6-7 should be equal to the other two added together.
Given my last message (thinking now you have a 18VAC CT secondary) I don't think your meter can actually measure such a small winding.

I removed the transformer from the board. the AC side now is just a cap with one leg lifted. I was just making a quick test to see if I could find anything obvious on the board apart from the transformer.

Yeah, my meter is a problem, actually. It was actually the first thing electrical I ever got. I do intend to get a better one in the future, but for now that's what I have available.

But, the three taps measuring the same resistance could be a sign of a short, no? I don't know what to expect in terms of resistance from the primary (in case it is the shorted one).

[pqass]

I removed the transformer from the board. the AC side now is just a cap with one leg lifted. I was just making a quick test to see if I could find anything obvious on the board apart from the transformer.

Yeah, my meter is a problem, actually. It was actually the first thing electrical I ever got. I do intend to get a better one in the future, but for now that's what I have available.

But, the three taps measuring the same resistance could be a sign of a short, no? I don't know what to expect in terms of resistance from the primary (in case it is the shorted one).

If you have a "relative" mode on your meter you can null-out the meter leads and try measuring all three pins again.
I'd expect each half to be of similar resistance to pins 1-2 (8VAC) but probably a little lower given the 6-8-7 secondary has thicker wire.
But, yeah, it may be shorted too. 

BTW: I measure 4.7 ohms across the leads of the main power switch (S3) directly in front of my [E3611A] transformer.
Yours should be the same if you're in 120VAC service area.

[TERRA Operative]

Here you go, because I crave acceptance and praise from random people on the internet , I measured the output side of the transformer in my 100V E3610A with my freshly calibrated HP 34461A multimeter in 4-wire mode.
The transformer was removed from the unit for the test.
(Values in brackets are my best guess at nominal values)

1-2: 0.357 Ω (0.36 Ω)

3-4: 3.798 Ω (3.8 Ω)
3-5: 7.563 Ω (7.6 Ω)
4-5: 3.762 Ω (3.8 Ω)

6-7: 0.202 Ω (0.2 Ω)
6-8: 0.111 Ω (0.1 Ω)
7-8: 0.092 Ω (0.1 Ω)

[augustol]

Here you go, because I crave acceptance and praise from random people on the internet , I measured the output side of the transformer in my 100V E3610A with my freshly calibrated HP 34461A multimeter in 4-wire mode.
The transformer was removed from the unit for the test.
(Values in brackets are my best guess at nominal values)

1-2: 0.357 Ω (0.36 Ω)

3-4: 3.798 Ω (3.8 Ω)
3-5: 7.563 Ω (7.6 Ω)
4-5: 3.762 Ω (3.8 Ω)

6-7: 0.202 Ω (0.2 Ω)
6-8: 0.111 Ω (0.1 Ω)
7-8: 0.092 Ω (0.1 Ω)

Oh my, thank you very much. You didn't need to do that. That's very helpful.

But yeah, my multimeter can't read resistances that low. For some time I've been considering that 0.8R as an "offset" and it kind of worked for some cases. For example, comparing my measures and yours between 1-2, there is approximately 0.8R difference.

But 0.1 and 0.2 my multimeter definitely won't be able to measure. Not even considering this "offset".

Anyways, I'm waiting for a reply from the guy that makes custom transformers. I've messaged him today in the morning. I guess monday I'll get a reply.

[pqass]

Here you go, because I crave acceptance and praise from random people on the internet , I measured the output side of the transformer in my 100V E3610A with my freshly calibrated HP 34461A multimeter in 4-wire mode.
The transformer was removed from the unit for the test.
(Values in brackets are my best guess at nominal values)

1-2: 0.357 Ω (0.36 Ω)

3-4: 3.798 Ω (3.8 Ω)
3-5: 7.563 Ω (7.6 Ω)
4-5: 3.762 Ω (3.8 Ω)

6-7: 0.202 Ω (0.2 Ω)
6-8: 0.111 Ω (0.1 Ω)
7-8: 0.092 Ω (0.1 Ω)

TERRA,
if you could measure the AC RMS voltages between those pins, then that would finally put to rest this discussion on the secondary center tap voltage.

Thanks.

[TERRA Operative]

Alrighty, here are the E3610A transformer output voltages.

Open circuit voltages:
1-2: 7.9V

3-4: 14.6V
3-5: 29.2V
4-5: 14.6V

6-7: 20.4V
6-8: 13.1V
7-8: 7.3V

Transformer installed with no load on output terminals and all dials set to 0.
1-2: 7.9V

3-4: 14.4V
3-5: 28.8V
4-5: 14.4V

6-7: 20.3V
6-8: 13.0V
7-8: 7.3V

[pqass]

Alrighty, here are the E3610A transformer output voltages.

...

Transformer installed with no load on output terminals and all dials set to 0.
1-2: 7.9V

3-4: 14.4V
3-5: 28.8V
4-5: 14.4V

6-7: 20.3V
6-8: 13.0V
7-8: 7.3V

Thanks TERRA.

Well, that settles it, that last winding has a similar 2/3rds-1/3rd split just like my E3611A.

augustol,
if rewinding doesn't work out, I still think you can opt for the 24VAC CT 80VA toroidal transformer https://www.digikey.ca/en/products/detail/hammond-manufacturing/1182M12/4809336 and add these additional secondary windings 8VAC, 30VAC CT, and a 4VAC.  Assuming 0.25V/turn***, that would mean 32 turns, 60 turns (of a pair), and 16 turns, respectively. The first two can be 24AWG but the last one should be at least 22AWG (5A capable).

Why the additional 4VAC? A:The full 24VAC may produce too much heat in the pass transistors so by connecting a 4VAC winding "backward" to the direction of the end lead, we can subtract those 4 extra volts.   This will get you to a 0VAC-12.5VAC-20VAC secondary as confirmed by TERRA.

It's not cheap though; CA$80.  But it's easier to wind secondaries than primaries.

***You need to confirm this with the actual transformer you buy.