Opportunity to buy an old valve guitar amp

[Refugee]

I would say that it is only worth it if you are buying for the name.
For functionality a couple of double triodes could be made up into an adapter with any good valve radio providing the power amp via the gram input. You also get two ways of driving it into distortion as an added bonus as the radio will have its own volume control in addition to the one in your add on unit.

[Bushbaby]

Nice to see you on the forum Rob!

If the loud hum is emitting from the speaker, it's unlikely the output transformer is shot. Much more likely to be the 20uF 450V smoothing/reservoir caps. Given the age of the amp (45 yrs), the cathode bypass cap (25uF/25V) will most likely be u/s too, and of course, it would be a wise precaution to replace the .02 cap feeding the 6V6 ('that cap').

Lots of domestic radios from the late 40s onwards used 6V6 output stage - sometimes, as in the Barker 88, two is push-pull, so in the unlikely event of the OPT being shot, one could be culled from a scrap radio chassis.

(I'm not sure from your post whether you've bought the amp Rob, or are considering buying it - the title of the thread suggests that you're thinking about it and wondering from the description of hum, if it's worth a punt).

This is another instance where someone has an irresistible urge to switch it on to 'see if it lights up' with the risk of seeing it light up spectacularly for a brief instant, sending it to the 'scrapyard in the sky'.

Hope that helps a bit.

Hi David,
Slowly returning to the land of the living. I am working on an a teacher training course ready to set up my own business.
I'm slowly getting back toward what I enjoy, pottering with radios and amps so I will be posting a wee bit more in future.
I haven't bought the little amp just yet but trying to weigh up whether its a viable proposition.

Best Regards

Rob

[AlanBeckett]

... so I will be posting a wee bit more in future.

Come, come young Rob, that's Scottish. In England now the correct terminolgy is 'littlebit' - all one word

Anyway, you still have to get your Lathe and giant EKCO going.

Alan

[Yorkie]

... so I will be posting a wee bit more in future.

Come, come young Rob, that's Scottish. In England now the correct terminolgy is 'littlebit' - all one wored

Anyway, you still have to get your Lathe and giant EKCO going.

Alan

Behave - we've all got a 'to do list'!!

[AlanBeckett]

I was simply pointing out young David that in the past our cousins North of the border were always going on about a wee this and a wee that and a wee the other, but now we've caught up with 'littlebit'. A skilled Sports Commentator can get littlebit four or five times in one sentence - If they play a littlebit further forward with a littlebit more effort and a littlebit more width they'll manage a littlebit more penetration etc etc.
Of course we all have a 'to do' list, and often a 'doing' list, but I don't see why I can't pull his leg about it. After all, I made the pulley for his Lathe and collected the EKCO.

Alan

[Bushbaby]

No offence taken at all. Ive also got a roundtoit list too. I've got a big one of those!

R

[valves4amps]

Hi Rob I've repaired quite a number of Fender guitar amps Bassmen and Champ's of that era. Some with hum turned out to be the fibre board they're built on becoming leaky, leaking ht where it shouldn't be. After the usual checks have been done, as has been pointed out, electrolytic and coupling caps, any residual hum if its at the front end, then lifting the input components from the board can cure it. Otherwise its a complete rebuild preferably on tag strip more point to point.

Dave.

[Yorkie]

... I don't see why I can't pull his leg about it. After all, I made the pulley for his Lathe and collected the EKCO.

Alan

Of course you can Al, and you were - we're all chums in this parish after all!

For the avoidance of doubt, I was engaging in a bit of leg pulling myself - not trying to be a self-appointed moderator

[Bushbaby]

Hi Dave,
Thanks for your helpful reply. I have some new phenolic board and tags so I could easily replace the board as necessary. I have concerned that I might be buying a pup that has something drastically wrong with it. The circuit for this model is similar to the original vibrochamp circuit but I believe the bronco runs at slightly higher internal voltages(?).

Many thanks

Rob

[Yorkie]

Looking at the circuit Rob, it's quite a simple design - the amplifier section is just one 12AX7 and the 6V6. The other 12AX7 is for vibrato, so can be disregarded as far as amplification is concerned. Then there's the rectifier valve and smoothing arrangement. (The three 20uF 450V caps might well be in one can or separate. 22uF ones would be the standard caps nowadays. Not sure if three section ones are available, but it makes no odds as far as getting it working is concerned).

Happy bidding - I can see this Amp making its way across the pond to Hockley!