Author Topic: Howard Valve Radio, Let's make it sing again.  (Read 4829 times)

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Online Cubdriver

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #25 on: July 10, 2016, 03:01:49 am »
Muttley, it looks like your big Howard has a push-pull output stage (the (2) 6V6s being the power tubes and the 12SN7 being used for the phase splitter to drive them.  The 5-series tube is the rectifier in both sets. 

Do they mount the audio output transformer on the speaker frame rather than the chassis?  I see only one transformer on each of the two different chassis, but one of the photos of the 'new' radio shows what could be a transformer on the speaker.

The 6V6 is a popular output tube; it's likely that someone pilfered the one that was in the new radio at some point in the past.  Either of those in your old set should work.  The suffixes on American tube numbers typically designate revisions and are usually backward compatible, electrical-wise at least.  The 6V6 was developed by RCA, and initially released as a metal tube (the plain 6V6 designation).  At some point, a glass envelope version was introduced (the 6V6G, popular lore seems to be that the 'G' stood for glass; these were the early 'coke bottle' tubes with the shouldered envelope and are physically larger than the original metal version and so may not be physically backward compatible with it but if they fit they'll work in place of the plain tube.  Next came the 6V6GT, this being a physically smaller version with a tubular glass envelope (Glass-Tubular being the explanation I've seen for the suffix) rather than the original shouldered version of the 'G'.  This was eventually followed by the GTA version, the 'A' designating some additional characteristic of the tube such as controlled warm up filament for use in series string arrangements or some other sort of improvement. 

TL/DR - the 6V6 in your big radio will work in the new radio.

Hope your migraine passes soon.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 
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Online Cubdriver

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #26 on: July 10, 2016, 03:03:58 am »
Muttley - just read the post you put up while I was working on my last one.  Excellent - glad to hear that it at least sort of works!  Fingers crossed that whatever caused the burn smell is minor.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Online tautech

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #27 on: July 10, 2016, 03:09:15 am »
Careful Muttley your new boombox might give you a real headache now it's going.  :-+

I dunno, these young fellas and their boomboxes.  ;)
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Offline Muttley Snickers

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #28 on: July 10, 2016, 03:16:56 am »
Just tried it again and no joy, whatever was causing the smell which I can only describe as slightly waxy if that's a term has caused the unit to stop responding, so as previously mentioned time to start getting a list together of required components and fortunately for me a good friend only five minutes away is a retired TV repairman with bins full of older components including capacitors, some of the values of which I certainly wouldn't have around here.
 

Online Cubdriver

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #29 on: July 10, 2016, 03:27:13 am »
Sounds like (other than letting the magic smoke out) you should be in pretty good shape, especially with the retired TV guy's assistance.   :-+  Keep us posted on your progress.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline vk6zgo

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #30 on: July 10, 2016, 03:53:12 am »

A bit of the existing wiring and number of solder connections on the unit are questionable and will require attention as well there is no mains power switch incorporated on any of the potentiometers and I may also look at addressing this as I do have a collection of switches and other switched potentiometers, the mains and fuse situation as previously pointed out without question needs to be tidied up but I am not sure if the chassis is meant to be earthed, our existing valve radio does have continuity between the mains earth plug and the metal chassis depending on where you probe, brass fixing screws seemed to be the best place.

They generally are Muttley unlike old TV sets that have a live chassis.
.

Live chassis BW valve TV sets are very,very rare in Oz---They almost all used a power transformer.
The only exceptions I can remember offhand  were a few early "portables" from Admiral,& perhaps Stromberg-Carlson,or Healing.
Maybe the situation in NZ was different.

Some country towns still had DC Mains in the '50s,so some AC/DC mantel radios were built for that market (pretty much as "special orders").
Apart from those few,the "all-American Five"  style of AM radio & its Brit & Euro equivalents never took off in Australia,as transformers were cheaper to make in this country than the extra insulation needed with transformerless construction,to say nothing of series string valves.
AWV & others turned out enormous quantities of normal 6v & 12v heater valves,& very few other types.

In any case,transformerless designs were very much frowned upon by Electrical Authorities.
 
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Offline vk6zgo

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #31 on: July 10, 2016, 04:29:45 am »
I could not believe my eyes when i came across ac/dc mantle sets , also those straight ac sets that were just ac rectified (no dc) , death traps !

I worked at Atkins (WA) back in the day----I was only a storeperson with apirations at the time.
Whenever one of those things came in to go to the Workshop,everybody shuddered.

One thing which I remember from that time was that Atkins were agents for AEI,who were selling Radios & TVs under the Ekco brand--All nice sets,& pretty much standard OZ style,despite the UK origin of the name.

The RM204 was a normal 5 valve mantel set,& the Workshop guys discovered the RF & IF stages would work OK with 32vDC HT,but the output stage was a bit lacking.

They replaced that with a transistor output stage,& changed one of the valve stages to  a 12.6 v filament type.

Quite a few of these were sold to farms with 32v DC lighting plants.
I'd love to find one--a definite collector's item.


« Last Edit: July 10, 2016, 04:31:24 am by vk6zgo »
 

Offline SeanB

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #32 on: July 10, 2016, 10:44:29 am »
Time to replace all the wax capacitors before any more power being applied, as you can very easily blow a screen grid on the valves, or burn out the transformer with a leaky capacitor. As well replace all electrolytic caps, especially the 100uF 16V ones on the cathodes, though there use a 63V part, as it will be the same size as the original.

then you can go resistor checking, mostly in circuit as they pretty much all have vacuum on the one side when power is off. If higher than the nominal value simply replace with a new 1W film for all, except for power resistors where you need a higher rating. 1W film simply because they are similar in size and have a high enough voltage rating so will not flash over or burn out.
 

Offline Muttley Snickers

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #33 on: July 11, 2016, 02:49:28 am »
Thanks Sean, yes after the sausage sizzle we experienced yesterday I wont be powering the radio up again until it is good, safe and ready to do so, I'm still having no luck finding the main PCB and microprocessor and thought they were hiding somewhere out of sight so this is now a mystery, it couldn't possibly work properly without them surely.

I had a bit of difficulty de-soldering a few of the existing condensers and didn't want to just cut them out in case they are still ok or if I cannot readily get hold of replacements, simply not enough tip area on the bench soldering irons to transfer the heat into the old connections, most of which were back onto the chassis itself so I resorted to the Weller Gas Pyropen which is always excellent for larger solder pads and these types of old crusty joints, it worked a treat.

The far left red capacitor in image 0517 was not connected at the displayed end and the remaining exposed lead appears to have been either cut, corroded or simply broken away, it's very hard to determine what occurred there but we did have the radio sort of working for a short period without it so I don't know about that one.

 

Offline lowimpedance

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #34 on: July 11, 2016, 04:06:50 am »
The one on the right in the first pic looks like the offending sausage   :D  (not sure the aroma would have been as inviting as the more traditional BBQ!).
 Its good to see some more 'vintage' stuff here  :-+ , particularly when most of the time all we get is micros, LCD's and highly integrated PCB's .......yawn.
The odd multimeter or 2 or 3 or 4...or........can't remember !.
 

Offline SeanB

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #35 on: July 11, 2016, 04:53:22 pm »
Do not try to unsolder the leads from the tags, just cut right by the body, and replace with polyester capacitors of the same ( or the next value up for those oddball ones) capacitance and with a higher working voltage. The lead stubs make fine ends if you use a small pair of needle nose pliers to make a loop to put the new lead through then solder in place. Same for resistors, much easier than trying to get solder off a brittle base that will crack if heated or moved too much.

 
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Offline Muttley Snickers

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Re: Howard Valve Radio, Let's make it sing again.
« Reply #36 on: July 12, 2016, 11:58:19 pm »
I'm going to start cutting the majority of them out this afternoon and have been taking a number of close up shots so I will know exactly where they were connected when putting them back in, a couple of closer pictures below of the main suspects, one looks to have been chewed by a rodent, another looks to be suffering from leprosy and the final one blew a fuse or something.
 


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