Ideas needed

[Toon]

I was given an old Roy amplifier with a shorted power transformer and broken tubes. I haven't been able to find any information whatsoever on this amp. It appears to be some obscure European brand.
The cabinet resembles the one of a VOX AC30 and it is really nice. It holds 3 pre-amp tubes (one for each channel and a mixing tube) and 2 pairs of power tubes. It's got 2 12" 16Ohm speakers wired in series.

I want to build a amp from scratch using the cabinet, the output transformer and speakers. Does anyone has suggestions as to what would be good project? The schematics I considered ( Bassman 5F6A, etc) seem to be incompatible with the speakers

Thanks,
Toon

[PRNDL]

The schematics I considered ( Bassman 5F6A, etc) seem to be incompatible with the speakers

The output transformer is selected to match the impedance of the output tubes to the speaker. If you keep the same output tubes and speakers, it should be fine.

The cabinet resembles the one of a VOX AC30 and it is really nice. It holds 3 pre-amp tubes (one for each channel and a mixing tube) and 2 pairs of power tubes.

You didn't mention what output tubes it uses. If they are EL84/34 a Vox AC30 would both sound and look great.

It's got 2 12" 16Ohm speakers wired in series.

You may want to check that again.

[Toon]

Hello,
Thanks for the input.

Originally Posted by PRNDL

The output transformer is selected to match the impedance of the output tubes to the speaker. If you keep the same output tubes and speakers, it should be fine.

Is there an easy way to tell if this output transformer would suit a AC30? I measured the resistance of the prim ( measured between center tap and one of th two terminals) and sec winding and the ratio is about 40. With a speaker load of 32 Ohm, this transformator could accomodate tubes with an output impedance of 1200 - 1300 ohm??

You didn't mention what output tubes it uses. If they are EL84/34 a Vox AC30 would both sound and look great.

I can't tell because the tubes were gone when I got the amp.


You may want to check that again.

I checked it and they are definitily wired in series

[PRNDL]

This is a difficult one, since the EL34 and 6L6 are almost identical in wiring. You may want to check how pin 1 is wired to be sure. Also check the chassis and cabinet for some kind of tube placement chart.

Are there multiple taps for the speaker?
I ask because 32 ohms is unusual, whereas 8 is extremely common.

Is there an easy way to tell if this output transformer would suit a AC30? I measured the resistance of the prim ( measured between center tap and one of th two terminals) and sec winding and the ratio is about 40. With a speaker load of 32 Ohm, this transformator could accomodate tubes with an output impedance of 1200 - 1300 ohm??

That does sound about right for two EL34's in parallel.

This is a hard one ... don't worry, there's bound to be posts from other forum members with more knowledge and experience.

[tubeswell]

on the EL84/6L6-6V6, question, you can tell if the amp has nine-pin or eight-pin(octal) sockets for these tubes.

4 x EL84s can get you 30watts @ 7.5 watts per tube or 50Watts @ 12.5 watts per tube, depending on how they are set up and matched with an output tranny. (Have a look at Peavey Classic 30 and Peavey Classic 50 amp circuits to get an idea).

4 x 6L6s can get you a whole lot more - depends what you want.

FWIW I think 30W is plenty loud enough for most gigs in the world. (I'm guessing they are all nine-pin sockets in there?)

[Albert Kreuzer]

Hi Toon,

the amp is German made from the 70s, never had one on the bench, but I've seen pictures of it.
IIRC it has 3 x ECC83 (12AX7) and 4 x EL34.

If you want to build something different, look at the Vox AC100 or the Selmer TnB100 - I always wanted to try one of these.
Also an Orange Graphic 120 MkII could be nice.

Cheers,
Albert

[Toon]

Originally Posted by tubeswell

on the EL84/6L6-6V6, question, you can tell if the amp has nine-pin or eight-pin(octal) sockets for these tubes.

The amp has 9-pin sockets for both pre-amp and power tubes

4 x EL84s can get you 30watts @ 7.5 watts per tube or 50Watts @ 12.5 watts per tube, depending on how they are set up and matched with an output tranny. (Have a look at Peavey Classic 30 and Peavey Classic 50 amp circuits to get an idea).
I 'll do this.

4 x 6L6s can get you a whole lot more - depends what you want.
I am considering an amp that is not too loud and that breaks up at a sustainable volume. I have played Fender Twin Reverbs and 100W Bassmans ( both Silverface unfortunately) and they are just too loud. My first idea was a Bassman 5F6-A of a Marshall but then I realised I would probably couldn't use the speakers and tranny. In the case of the 5F6-A, the cabinet couldn't accomodate 4 speakers

FWIW I think 30W is plenty loud enough for most gigs in the world. (I'm guessing they are all nine-pin sockets in there?)

Right!

[Toon]

QUOTE=Albert Kreuzer;52390]Hi Toon,

the amp is German made from the 70s, never had one on the bench, but I've seen pictures of it.
IIRC it has 3 x ECC83 (12AX7) and 4 x EL34[/I].[/LEFT][/LEFT][/I][/I]

Great! Thanks for the input. I am so glad the mystery has come to an end: a German amp from the seventies. It doesn't hold a rectifier tube but uses two diodes instead; makes sense for a seventies amp. It use to be a bass- organ amp.
If you want to build something different, look at the Vox AC100 or the Selmer TnB100 - I always wanted to try one of these.
Also an Orange Graphic 120 MkII could be nice.

I will look into this. I am looking for an amp that breaks up at a tolerable volume. I considered a Bassman 5F6-A ( with effect loop) or a Vox AC30 ( incl. tremolo circuit) The Orange amp intruiges me. Never played one though. What is your experience with these amps?

[Albert Kreuzer]

Originally Posted by Toon

What is your experience with these amps?

LOUD.

[Two Tone]

Those are great amps,rumour has it they were build by one of the
founders of Kitty Hawk.
I wouldn´t mod the amp,I had 2 of those for repairs,
both were 1:1 copies of an AC30(but for the tube rectifiers)
Only weak parts were the speakers.
They sometimes show up on the Bay