D718 & B688 Transistors - Substitutes?

[redwire]

Re: D718 & B688 Transistors - Substitutes?

The Technics design looks good, worth restoring. New stuff is so cheap and sounds terrible, hard pressed to use five transistors per channel and overheats.
The FET phono preamp is nice, I would put in a better op-amp than NJM4559.

Polar vortex is usually on top of us, or the UK when the gritters come out. -33C last night, time to fire up the tube amplifier.

[budm]

Re: D718 & B688 Transistors - Substitutes?

I would suggest to put 75W incandescent lamp in series with the AC Line feeeding the unit incase there is is still problem with the circuit so you will not blow up your new Transistors.

[Nevillet]

Re: D718 & B688 Transistors - Substitutes?

The transistors arrived today and it's working well apart from the volume and balance. I've tried cleaning with Servisol contact cleaner but they're less than perfect.

The amp smelt like an ashtray when it arrived and i've managed to clean most of it off bu not inside the pots which may be the problem.

On the schematic the Vol is marked as 100K (B) and the Bal as 100K (G)

I guess the B & G refer to the types of taper. I get a bit confused with pot tapers and there doesn't seem to be consensus.

Can anyone advise.

[R_J]

Re: D718 & B688 Transistors - Substitutes?

Google can help https://eepower.com/resistor-guide/r...iometer-taper/
"A" LOG, logarithmic
"B" LIN, linear
"G" taper (Graphic taper) G taper is reverse audio till midpoint and regular audio after that

[Nevillet]

Re: D718 & B688 Transistors - Substitutes?

Many thanks.

I've used log & lin pots but not graphic taper. I thought that for audio volume controls log pots were used. I need to search my usual UK suppliers for the G pot (as opposed to the mythical G spot)

I've read the EEPower page you linked to and it was clear - apart from the variance in marking codes.....

I have a 120W (240V) lamp downstream of a variac to power the amp whilst on the bench and have been using it till now (& until i've proved to myself I hadn't mucked it up)

I have to say the amp sounds really good with a CD player and driving a smallish pair of HiFi speakers.