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What class is my el34 amplifier

I recently became the owner of a pair of tube monoblock integrated amplifiers that were custom designed and built for a local discriminating audio enthusiast. I don't know why but he never used them and has moved from the area so I'm unable to contact him for more info or to find the builder. These amps have 4 EL34 pentodes each with a switch of unknown function. I have owned two Cary amps both of which had similar switches allowing a choice of running the amp in ultra linear or triode mode. It makes sense that is the same. The other option could be to accommodate a different tube, I suppose. Even though these are integrated I'm using them as power amps powering Martin Logan Ethos speakers. They sound wonderful especially in the upper mid frequencies. 
Anyway, I'm using them and they're beautiful and sound great but I would really like to know more about them. I don't have schematics so I'm just looking for suggestions re what these switches might do. 
128x128broadstone
12 responses Add your response
stereo5's avatar
stereo5
6,405 posts
 
Perhaps if you take some pictures inside and out and provide a link to the pictures, one or more of our tube experts may be able to help identify.
jond's avatar
jond
5,845 posts
 
Yes a photo and more info on the amp in general would help. What's the rest of the tube complement? Any identifying logos on the transformers or anything?
atmasphere's avatar
atmasphere
11,841 posts
 
If you have to set the bias, the bias current would offer a clue. The input tube complement would offer some information about that as well. Its a pretty good bet that they are class AB1 though.


broadstone's avatar
broadstone OP
310 posts
 
552424213.jpg
broadstone's avatar
broadstone OP
310 posts
 
I’ve not had luck with photobucket yet. When I do I’ll send images. 
jond's avatar
jond
5,845 posts
 
Broadstone you can also create a System page here and post photos to it.
broadstone's avatar
broadstone OP
310 posts
 
Ok, I created a system page (Broadstone’s system). The output tubes,4 per amp, are 6L6’s; the input is 6EU7. Each amp has a 2 way toggle switch of unknown function and a standard VU meter @ -20 to +5 range. I hope this helps. 
broadstone's avatar
broadstone OP
310 posts
 
My apologies for wasting time on this issue but lm unsuccessfully trying to submit images using the procedures suggested. Anyway, based on the above description, does anyone have a suggestion re the possible class and what the switches might control. I can send images by email or text if anyone would be willing to view them via that method. Thank you
atmasphere's avatar
atmasphere
11,841 posts
 
The amp sounds like it is class AB1. Is there also a control, perhaps adjusted with a screwdriver?
broadstone's avatar
broadstone OP
310 posts
 
 Atmasphere, first, thanks again for your past help when i was using Cary amplifiers with my Odysseys. There is no external  control other than for volume   the only adjustmentl inside the chassis is on a small circuit board and I think appears to be for the VU meters. BTW, this is my 4th tube amp and it produces much more heat than any of the previous ones. Could this be another possible indicator of class A operation?  This goes to the question of the unknown switch possibly set on triode mode??
broadstone's avatar
broadstone OP
310 posts
 
My images finally appeared under "broadstone's system"  I hope this helps. 
atmasphere's avatar
atmasphere
11,841 posts
 
If there is no adjustment its either got some form of Bias regulation or its class A, being cathode biased. If the amp does not have a circuit board that looks fairly sophisticated, its likely the latter.
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