Request for schematic and PT specs for Sonaro combo

[BryndynW]

Hi all,
This is my first post so be gentle.   I searched through the forums and wasn't able to get my question completely answered so hence the post.

I'm trying to get a Sonaro combo working again but it appears to have a bad power transformer.  Looks like a Schumacher model 28-2340.  Can anyone recommend a suitable replacement or the technical specs for this PT?

I have not been able to locate a schematic for this amp online.  Closest I've found is one for the Sonic I-40 head.  Does anyone have a schematic for the Sonaro they would be willing to share?

Thanks a lot,
Bryndyn

[loudthud]

Sonic I-40 schematic is probably the correct one. Search this site and you can find answers to most of your questions. I searched for "replacement transformer" and found the info you need in under a minute. Go Here:

http://store.yahoo.com/triodeel/

Clinc "Dynaclone transformers" and order a PA135. Should be exactly what you need. 40W Sunn amps used a Dynaco Mark 4 power amp.

[BryndynW]

Thanks loudthud.  I had already checked out the information on Triode's website but wasn't quite conviced that it would be a direct swap.  The info for the PA125 indicates a 55V bias tap.  Do you know what this value is for the Sonaro?  Is this a completely different "bias" than the output tube bias which is indicated as -34V on the Sonic I schematic?

I tried to reach Ned Carlson at Triode a couple of times yesterday but we didn't connect.  I'll try again today to see what he thinks.  

I also spoke to Dan Torres (Torres Engineering) and he felt it would be possible to use a Hammond 273BX but the bias would need to be changed.  I don't know how to do this so he said he'd be willing to draw up a diagram for me to follow.  I'll opt for the path of least resistance and post my findings/results.

BTW, Schumacher was not able to provide the technical specs for the PT used in the Sonaro.  They couldn't find any records for the model number (28-2340).

Thanks again.

[Anonymous]

I looked at the possible Hammond replacements and the 273BX was the closest but it's a little bigger. The 373BX has the bias tap but it's even bigger and has a universal primary and 50 or 60Hz rating. I got a replacement from Triode for a 200S and it was an exact fit. The -34V bias is adjustable and the number on the schematic is just a ballpark value. It needs to be adjusted for your individual tubes. (Hint...search this site for "bias"). I'm assuming that you have a 40W chassis that used EL34-6CA7's.

[BryndynW]

Yes that's right, it's 40W RMS with twin EL34s.

I spoke with Ned Carlson at Triode last night and he thought the PA135 Dynaco clone would be just about an exact match so I ordered one.  Now I'm beginning to doubt whether or not 1) the PT in there now is the original since it has a date of Feb 1970 and the amp is from 1967/68 and 2) the PT is from Schumacher as I had thought based on info I scrounged from some other threads.  I can't find a 606xxx number on the unit and a Schumacher rep said he couldn't find anything matching the amp model or the code on the PT (28-2340).

The bias issue is becoming clearer the more I research (I'm a novice with amps but don't worry, I learned how to at least bleed the caps).  The local repair guy helped me confirm that this amp has an adjustable bias yesterday.  Now I just need to figure out from where to take my measurements during the re-bias process.  I'll continue to scour this forum for that info.

I'll let you know how the PT transplant goes.

Thanks,
Bryndyn