rebuilding 80B with transistors

[mell]

hi,
we have a trident 80B without the transitors , this one is from 1987, the previous or earlier 80B version had BD517 BD518 BD519 BD520, we tried a replacement but the channel crackles when i push mute and pannorama switches, ...i suspect i got the wrong types,eventhough the specs match , more or less ...

now the question is, is there anyone who has rebuild their channels with the transistors WITHOUT these problems, if so WICH transistors did you use??

thnx in advance
melvin

[Jim Williams]

I use the On semi MJE172/182 pairs. Those are very linear and fast. They do 3 amps max. Pinout is different. I also rebuild the drive section and replace the 2 diodes with 2.2k resistors. Then I use either a red LED or a pair of 1N4148 diodes in series from base to base for bias. That lowers the current drive stage THD to below .02%, the stock config does around .4% as Trident designed it. Use a precision opamp and those coupling caps can go, permanently. Now you will have very punchy low end and that direct coupled sound, pure and clear, DC to 200k or so.

[mell]

hey jim thxn for the reply!!,
as u may have noticed capstan cappy on GS and me are one and the same, ...
i will try your suggestions and report back on the result.

mell

[Jim Williams]

Here's more detail so it will work. Change R75/77 to 10k. D8 and D7 should be 2.21k. R74/85 are 15 ohms. Q6 is MJE182, Q5 is MJE172. C30 is replaced with a 56.2 ohm resistor. I suggest using Dale CMF60 resistors. Connect 2 1N4841 diodes in series base to base. Observe polarity, cathode to Q5. Use a low offset opamp for IC10 like LME49710, AD8597, OPA1611, AD4627-1 etc. Add a pair of .1 uf mono ceramic caps from pins 4 and 7 to ground. These numbers apply to the input module.

This is a "Williams" linearized class AB output stage, THD is very low compared to the original design that feeds the signals through the biasing diodes. If you want the original "crunch", just keep the original values and use the MJE transistors.

[mell]

hmm i could have sworn i replied yesterday, :|

anywayz
thnx alot jim! much apreciated!! ,
i have to get back to that studio soon to recap the EQ section , a couple of poweramps and some monitor crossovers, as you can guess the stuff is realy old hehe..will report back with my findings , may take a while,

many thnx!
melvin