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.
There are very few circumstances where one can simply drop in a tube as a direct replacement for another. There's more to it than having the same pinout. The operating point will be different, sometimes disasterously so. At the very least, the sound quality is likely to change, probably for the worse.
How about a simple voltage divider at the input to lower the incoming signal level?
i do not know how much gain you want to reduce
a lot of gain reduced it needs change in circuits
add a voltage divider, or potentiometer, or change the value of rplate to a lowered value
but if gain to reduce is just a little bit so....try this!
there is many manufacturer produce ecc88 and they have a average gain of 33, but they are not exactly 33, maybe you should try another manufacture if you want to reduce just a little bit of your gain
i have a preamps contain singestage grounded cathode without capacitor decoupling using philips e88cc, and i replace it with sylvania 6dj8(ecc88 compatible) and i got a lowered volume as a result, i believe it gain lowered in a scale of 5 under ,but the sound change more bright, i do not know you would like the change or not, but the gain is lowered for sure.
Good idea, very good idea! But removing a possible cathode cap is dangerous ,you never go back even if it turns out you have not enough gain now .... sonics , a cathode cap is a coupling cap and the best coupling cap by far is no coupling cap at all.
very good sounding tubes are:
ECC99 , gain of 22, Gm of 9.5 mA/V @18mA, made by JJ only
5687, gain of 17-18, Gm of 8.5 mA/V @23 mA
6900 (see 5687), military version of the military version, could also be used as bullet , said by insiders to be the best sounding indirectly heated small signal tube, forgetabout fancy $$$ 6SN7 and the like.
But, price is fancy, too.
Consider you have to change the pinout. You have to run these tubes at those fat currents mentioned above and your PS has to be able to feed that. The ECC88 also loves relativly fat current (10-12mA), it should be used that way for audio although very often it is not
Anyway it is a circuit change required for trying these tubes.
The only topology i know of where you can plug different tubes into w/o damaging anything and with getting fair to good results is the classic SRPP stage.
Don't change the tube. You can put a resistor in series with the pot. For example - if you have 150k pot in front of the tube - you can change it for 50k resistor and 100k pot in series. That will lower the gain of the whole circuit.