• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tamura F2011/el34 x 4


2010-02-16 9:00 am
I just designed a pcb for an universal PP amplifier.
The schematic for 5881 / 6L6 is this:


I tested this circuit with 6V6, 5881, EL34 and EL509 and it works perfectly.
(ofcourse with different OPT's)

You can omit C8 and R22 and you need to determine the value for R6 (about 3k = 16 dB GNFB).
This resistor determines the amount of GNFB. Also C3 can be omitted with good output transformer.

With UL connected EL34, 4k to 8 ohms OPT and 450 V supply voltage, the output power was some 40 W.
With pentode connection and 500 V anode-/400 V g2-voltage, the output power was some 65 W.
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2008-08-16 4:57 pm
I would like to recommend one of these schematics, available at tubebooks.org
I tested them myself, with very good results.

Williamson (combine enhancements from these 2 for best result):
"Modernize your Williamson" by David Hafler
"Improving the Williamson Amplifier" - Talbot, Wright

An Approach to Audio Frequency Amplifier Design, G. E. C. Valve and Electronics Department
Look for amplifier codenamed "88-50"

You can swap output tubes used in these builds with EL34 and corresponding output transformer, adjusting bias accordingly. I tested them with 6550, KT88 and KT120.


2010-02-16 9:00 am
Thanks guys,i looked into it a little bit,what i am after is paralleled el34 push pull,thanks again

Then you should just add an other pair of output tubes, each with own grid stopper resistors. The transformer impedance should be halved.
If you want to get good performance with your 3k5 Tamura, then the supply voltage should be not less than 500 V.

Do you plan to use UL or pentode ?


2009-07-29 3:14 pm
Thanks Artosalo,i was thinking UL and to be honest i dont have much expirience and knowledge when it comes to tubes(few tube buffers but mainly transistors so far)
So I'm really looking for some ready made(tested) schematic cause I'm really unexpirienced with tubes.
Thanks again


2010-02-16 9:00 am
A "ready made/tested" circuit is such that should be built with exactly the same output transformer and tubes.
For example to change the output transformer to similar impedance but other type/manufacturer may require some modifications, which are usually not very problematic, but require some knowledge and test equipment.

As an example; I have built tube hifi-amplifiers in small series. Although I use exactly similar components to all amplifiers I still need to do some adjustmets and use test equipment to get the best performance.

It is difficult to think a situation when an inexperienced hobbyist without suitable test equipment could get excellent results when a lot of modifications are needed.