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Just bought an already assembled 18 w head. Sounds great but how do I know what model it is? The guy said it was a 6v6 and he changed it to 6l6 and a 5Y3 rectifier. I brought it to a shop and the guy swears the power tubes are EL34's. It has 3 12ax7's in the preamp section. I can take pics. I just don't wanna blow this thing up...

Pics would probably be a good idea.

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Deric®

Beautiful build whatever it is

Joe G

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Some assembly required,
Brain sold separately...

Well, it sure looks like a JTM 45/plexi circuit and not an 18 watt for sure. Fixed / dual bias, presence control are the clues. Output tube wiring same as JTM45 except using a 1K5 resistor to grid on pin 5.

edit 6V6 grid is also on pin 5, so could be 6V6 or 6L6.

This is not a 'standard' 18 watt.

If you like it, that's what matters.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Here's the information from the original post:

Custom 18 watt marshall style amp. Sovtec 12ax7 pre, Sylvania 6V6 power tubes, Sylvania 5Y3 rectifier

The preamp circuit is like a Marshall 1987 50 watt - split cathode and non-master.

Specs are similar to what would be found in the early 70's Marshalls. The output stage is also very similar - push-pull with fixed bias.
tube rectification so that the B+ voltages can be manipulated by swapping different tube types.
A solid state replacement can also be swapped into the rectifier
tubes' socket for a big voltage gain.

The grid resistors for the gain stages have been soldered directly to the tube sockets and are wired with shielded cable for low noise operation.

Not convinced on the Output tubes tho.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

So I guess this isn't a Trinity? I like the sound but my tech says a 5Y3 rectifier tube will not work with the EL34's he thinks are in the amp.

No there are no markings on the tubes whatsoever. I just wanna make sure Im running the right rec and power tubes in this amp. Is there anyway I can tell.

Thanks for all the help so far. I am going to purchase the matchless type kit from here soon. Just wait for all those questions.

see my edit above, It could be a 6V6 or 6L6. The 5Y3 would be fine for the 6V6 but would use a GZ34 / 5AR4 for 6L6.

Looking at the transformers, not sure they are big enough to handle EL34 or 6L6.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

How hard would it be to convert back to a 6V6 tube? Would it just require a biasing when done?

Yes, that should do it.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

So I got the plate voltages from tube pins 3 and 8 (395) and installed the 6V6's but could only get them to 11.4 ma which is no where near wear they should be. The amp sounds great but what should I do to get the bias hotter.

It's a fixed bias amp so you need to carefully adjust the bias pots.

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

Not sure I understand. If it's fixed why does it have bias adjustment pots? I think I need to change the resistor values but to what I am not sure? Any ideas?