Parts Salvage Question

[Don Moose]

One of the 'top' pics makes the RCA look like it has a quad of 6BQ5s, so I think you have a stereo pair of 10-15W power amps there, and enough heater current to run 2 phase inverters and 2 more preamp tubes - look them up and note their heater currents - 12AX7s running on 6.3VAC want 300mA per tube.

Remembering that I'm a feature creep, I'd probably do something like a Fender Blackface preamp - the vibe channel of an AB763 deluxe - or something like a Vox AC30TB preamp - and then run an FX loop with a stereo return.

But that's just me.

Hope this helps!

[HJW]

Gentlemen, thank you for taking time to offer suggestions. I'll pull the preamp chassis later today and post a pic or two of it. Again, the RCA is just a phonograph console, so perhaps the preamp chassis will be usable as well.

I'll have to get busy and research some of these terms and such. I've got a mutimeter and I know how to solder, but unless I'm 100% sure about everything and understand exactly what you folks are suggesting, I may just gather the suggested possibilities and let an experienced tech do it.

But I'm a patient guy, and I'm fascinated by this stuff. And I've got a couple of guitar amps, so no need to rush.

btw, does anyone know if there is a source in or near Louisville to get the cans ? Peerless Electronics perhaps ?

And safety-wise, is it just a matter of pulling the cans as you would a tube ? Do I need to discharge them first or do I just grab them and lift them out ? I can't tell by glancing at the bottom of the chassis if they have pins like a tube.

Charles

[Gtr_tech]

The can caps are soldered to the chassis. 100w min iron or gun to remove the tabs. I'd just replace the cans with seperate caps. Price the new mfgr cans and you will prolly agree.

[HJW]

The can caps are soldered to the chassis. 100w min iron or gun to remove the tabs. I'd just replace the cans with seperate caps. Price the new mfgr cans and you will prolly agree.

Ok, thanks. So we're talking filter caps ?

I've decided to just take it to a tech. I'm dreaming thinking I can do it.

[Gtr_tech]

Yea, the silver cylinders are filter caps with 2 or more caps in each can. They're spendy. Keep in mind before you go sinking a bunch of money into this chassis, yer gonna need a preamp with a line level output to drive it. And....if you wanna use it with a regular guitar spkr cab you'll need to remove the output tubes from the amp section that won't be used. It did come from a 2 ch stereo console right? Never run a tube amp with no load on the speaker output.

[Gtr_tech]

BTW, here's the schematic for your amp chassis. See page 2.
http://techpreservation.dyndns.org/b...CA%20PM-18.pdf

[HJW]

Yea, the silver cylinders are filter caps with 2 or more caps in each can. They're spendy. Keep in mind before you go sinking a bunch of money into this chassis, yer gonna need a preamp with a line level output to drive it. And....if you wanna use it with a regular guitar spkr cab you'll need to remove the output tubes from the amp section that won't be used. It did come from a 2 ch stereo console right? Never run a tube amp with no load on the speaker output.

BTW, here's the schematic for your amp chassis. See page 2.
http://techpreservation.dyndns.org/b...CA%20PM-18.pdf

Thanks, yes, it's a phonograph console, no tuner. Can you tell by the schematic if the preamp chassis can be modded for a guitar preamp ?
I'm going to pull it out later and take some pics.

Got it on always having a load. I've actually disconnected(clipped the neg wire) on the internal speaker in an old Sano combo amp I have and I just run a cab plugged into the ext speaker jack. I have a label next to the power switch to remind me to make sure the speaker cable is plugged into it and the cab.

I'm not sure how to search for cap prices. How much difference in price are we are talking ?

[olddawg]

OK...so this old beast has a stereo power amp with two open ended EL84 (6BQ5) amplifiers powered from a common power transformer. Here is what I would do. I would use the power transformer and reconfigure the two EL84s and a couple of 12AX7s to build an 18 watt Marshall clone or a VOX AC15. Probably a Lite IIb or such. You would have to buy or scrounge an appropriate output transformer since the two that are there are too small for a push/pull 18 watt amp. With a little luck and skill you can probably reuse the chassis. I would recommend using new ceramic tube sockets (although it's up to you), pots, jacks and components. Using a turrent or eyelet board would also be advisable. Still, you have the basis of a nice inexpensive little screamer here. Before you start check out what the B+ is. Keep in mind that it will be a little higher if you use an SS rectifier to free up heater current for another 12AX7.

I stand corrected. It is indeed a quad of 6BQ5s in the output. Two PP amps not single ended amps as I thought. You could make an AC30ish amp with these parts and an appropriate output transformer.

[Gtr_tech]

Thanks, yes, it's a phonograph console, no tuner. Can you tell by the schematic if the preamp chassis can be modded for a guitar preamp ?
I'm going to pull it out later and take some pics.

Do you have the preamp chassis? If you do, you'd have to completely rebuild it into a guitar preamp. 6CG7s are nice for reverb pan drivers, but not really good for gain stage use.

If you obtained a guitar preamp with a pretty hot line out (+4 to +10db) you could run it directly into the pwr amp chassis, but it may not drive it to full output.

I think you may be better off having an amp built out of the parts you have (transformers, sockets). That way its on 1 chassis and easier to use/carry around.

Those output tubes you have just may be Mullard made and rebranded RCA. Be careful with those....they're worth decent money if actually Mullard tubes. Hell...even if they're not Mullard they're still worth money.

[HJW]

I stand corrected. It is indeed a quad of 6BQ5s in the output. Two PP amps not single ended amps as I thought. You could make an AC30ish amp with these parts and an appropriate output transformer.

Where would I find an OT to do it ?

How about the preamp ? Are there any tube pre kits that would work that sort of project ?

There seems to be a lot of room on the chassis, both bottom and topside.

[HJW]

Do you have the preamp chassis? If you do, you'd have to completely rebuild it into a guitar preamp. 6CG7s are nice for reverb pan drivers, but not really good for gain stage use.

If you obtained a guitar preamp with a pretty hot line out (+4 to +10db) you could run it directly into the pwr amp chassis, but it may not drive it to full output.

I think you may be better off having an amp built out of the parts you have (transformers, sockets). That way its on 1 chassis and easier to use/carry around.

Those output tubes you have just may be Mullard made and rebranded RCA. Be careful with those....they're worth decent money if actually Mullard tubes. Hell...even if they're not Mullard they're still worth money.

Heh, you posted as I was typing. Yes there is quite a bit of room on the power amp chassis. I'm getting ready to pull the preamp chassis here in a few minutes.

[HJW]

Gtr, would the Mullards have been marked "Made In USA " ? These do and have 59-39 under the MIUSA stamp.

EDIT: correction, it's 59-39 under the made in USA stamp on the bottle

[HJW]

These have +10db output and I was thinking of getting one for recording.
Applied Research & Technology: Tube Mic Preamps

I'd rather do as you say though Gtr, have it all on 1 chassis.

[Gtr_tech]

Scratch that....those are not Mullard made. Forgot about the circular plate stamp the Mullards (and Philips) have.

[HJW]

Scratch that....those are not Mullard made. Forgot about the circular plate stamp the Mullards (and Philips) have.

I just spend 20 minutes reading up on them and came back to post the same finding. But I learned a few things on the EL84, so it was worth it. D shaped getter, seams, etc. Good stuff to know. It made me look closer at one of mine.

I assume the halo/ring at the top is the getter ?