[Simon Young]

Hi
having problems with an Hartung OTL monobloc amps. The left one is ok but the right hand one the bias pot doesn't work.
The schematic shows 3 bias pots but I can only see 2.

[Simon Young]

[Simon Young]

I'm getting 5.6mv where It should be 0.00. I've changed the 6c33c-B and the preamp tubes; I was told they should be matched.
Just a bit concerned that I might damage speakers.


Any advice would be very grateful.
Simon

[FullRangeMan]

This circle are for introductiond only, Iam moving this topic to The Lab Circle.
Please introduce yourself to the community by starting a thread here. If you are new to the site, threads posted here will be approved more quickly than anywhere else. Please DO NOT start more than one thread.

[FullRangeMan]

The schematic shows 3 bias pots but I can only see 2.
Seems to me this it is a builder error at the assemblage.
I was told they should be matched.
What matched? the 6C33?  there is no 6C33 matched, unless you have hundreds of these valves to look for match and lots of free time, the output impedance vary from 70 to 120 Ohms, nominal 90 ohms. Even there is no tube tester to fit 6C33 tubes unless at the Ulianov factory.

Take care to handle this amp as rubber gloves, no rings or watches etc, the voltages are deadly, OTLs are extremely difficult to adjust.
http://www.hartung-amplification.com/page3.html

[Tyson]

Be extremely careful with that amp - the voltages that a 6C33 runs at makes it VERY dangerous.  A death trap, if you don't know what you are doing.