• 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.

EL84 matched pairs

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I am building a valve amp (not my design) which is supposed to have two sets of matched pairs on the output (EL84's), the application is for a guitar amp, can someone tell me how crucial it is that I make sure I use matched pairs and what the result would be if I didn't? Also are there good cheap modern equivalents of the EL84 available (in U.K.)?

Many thanks for help

Watford Valves have 12 different types of EL84 in stock and will match them for you. Just choose some that fit your budget (£7 to £20).

How affected the amp will be by mis-matched valves, depends on the design. Designs with common cathode resistors are most affected.

The Svetlana SV83 is a close cousin, and was available cheaply for a while. Can't seem to find any now.
Re: contact info please

Indy335 said:
Thanks for all your input guys. I have tried to find JJ Electronic manufacturing on the web and/or phone number but I can't find either. Can anyone tell me how to contact them.




Better buy from some distributor near you than directly from JJ... also because I think they sell only big stocks.
2nd (3rd?) the recommendation to to use JJ EL84s and get matched set.

I built a Morgan Jones EL84 Ultralinear Amp a few years back. Started with unmatched Sovtek EL84s, changed to matched NOS 6BQ5s and finally a matched quad of JJ EL84s (over a period of about 6 months). The JJ's were clearly the best.
BTW my bias scheme is ring of 2 transistor current source in each cathode (i.e. cathode biased) set to 38mA with 470uF/50V Blackgate Standard bypass caps.

With cathode bias it is very easy to check/monitor the matching - just check the bias voltage developed at each cathode. All of mine are within 0.1V with as typical value of 9.8 Volts.

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