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What is a good value for B+ ripple on 480VDC
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John Heath:

--- Quote from: Planobilly on December 03, 2016, 06:46:06 am ---Thanks guys for all the feedback. The hum turned out to be from something I screwed up in the bias supply.

The amp runs AB push pull and yes 480 VDC plate voltage is high. We push these tube past the normal limit all the time in high gain amps. Keeps the repair guys working...lol The heaters are AC on the  4 output tubes and DC on the 7 preamp tubes.

Also looking at several other similar amps, it appears that < 2% ripple is pretty normal for just the B+.

I am pretty new to all this and this is a fairly complex amp to build on a turret board at least for me. Here is a photo. I am still experimenting and have several issues to solve.



Thanks,

Billy

--- End quote ---

That looks like a nice amp. Well built on par with a fender or marshal. And a big thumbs up for taking it on. Watch out for the 480 volt power as it will definitely get your attention if you touch it. Also cool radio shack meter. It will log data if you have a computer with a com port. This is good to monitor AC current going to the amp for 24 hours to check for thermal runaway issues in the output. 
Circlotron:
A bit of ripple on the anode supply to the output tubes is not a big deal because being beam tetrodes (same with pentodes) the anode appears more or less as a constant current sink. A change in anode voltage produces very little change in anode current. Look at the characteristic curves and you see they go up vertically and then fairly horizontal. horizontal means large change in anode voltage but little change in anode current, so causes little hum to be sent to the output tranny.  A triode is much different in this regard. Also, as has been mentioned, a balanced push-pull circuit rejects hum from the DC supply.
Planobilly:
Thanks so much guys. There is a lot in you post for me to read and think about.

I think I will go back to AC heaters for everything. The way things are hooked up now all the voltages on the tubes are very good. It is currently biased at 40ma. Both channels are working more or less normally as far as I can tell. I still have some hum but I have not redone the lead dress to the preamp tubes. I have not tested the reverb yet or have the effects loop hooked up. Also the NFB is not hooked up yet.

I am not sure if the volume control on channel two is working correctly...I was never sure just how the channel two controls would interact.

I am building a little PCBs for the channel switching atm.

This is a really complex amp for my level of experience. I think this amp could prove to be a difficult build  for most anyone. For sure I am in the deep end of the pool..lol

The power transformer is a Mercury Magnetics APS FTW135-P. HT is centered taped and the AC voltage is 186 VAC to CT for 372 VAC total and rated at 750 ma. 55VAC bias tap. 6.3VAC filament tap rated at 7 amps. The output transformer is a Mercury Magnetics Tone Clone O100JM-VZ. Pretty pricy stuff...I hope it is worth the money.

Cheers,

Billy
calexanian:
Based on that you may want to eliminate that fuse and connect that tap to the mid point of your main filter caps. http://www.thevintagesound.com/ffg/schem/twin_reverb_sf_135_schem.jpg
Have a look at how it is implemented here.
JeremyG:
Hi Planobilly and everyone,
Nice construction of this amp, everything is clean. :-+
In the schematic, there is no ground connection on the output tube cathodes. Is it present on the actual construction?

For safety reason, I suggest you to place 2 serie resistors (100k or 220k) accros the capacitors C37 and C38 (one resistor for one capacitor, like on the schematic posted by calexanian) because if the fuse blow, you still have the lethal votlage accros these capacitors.
Also, the middle point of R72 and R73 should be connected on the middle point of C39 and C40 for sharing the voltage accros the capacitors.

As pointed out on previous posts, the push-pull topology is pretty immune to ripple if the transformer is well designed and the outputs tubes well matched.

Ps: sorry for my bad english  :(
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