Affordable Valve Company - Re-bias

[nathanjh13]

Hiya, thanks for reading.

I have a few amps, OTL, solid state and tube (tube being my preference by a country mile of course) and I need to re-bias my KT88 integrated amp after a valve change.

The readings aren't "too" different but I wanted to confirm with somebody in the know that these are the right adjustment points for the bias setting please (see pic).

I'll then plug the meter back in and adjust away.

Many thanks

[nathanjh13]

The values I've just checked are:

Left Rear 31.1
Left Front 34.7
Right Rear 31.4
Right Front 28.8

I suppose left rear and right rear look "matched" but i though the values for all would be higher that that anyway...

Am I talking sense or should I get someone else to sort this out, the procedure looks straightforward enough on the photo but I'm clearly dipping my toe in the water. I need to dig out a spec sheet to look for the required bias value and set all to that? (Electro Harmonix KT88)

Thanks
Nath

[harwoodspark]

You're doing ok so far. As you say, you need the spec sheet and set each valve to the same bias current. Be aware that adjusting one valve can slightly alter the other of the same pair so you need to go through the op a couple of times leaving a settling period in between. Make sure you leave your speakers plugged in or use a dummy load and have the input unplugged.

[nathanjh13]

Thanks for taking the time to reply. Noted.

As for the settings I'm still a little blind, the company haven't written back with the values to use (I think they're funny as I didn't buy valves etc through them) but I'll keep looking.

I couldn't find Electro Harmonix spec sheets for KT88 but I'll look again.

All of the valves have "PC 81 TC 8" written on them.

Do I set the BIAS to 81 for all?

[harwoodspark]

Don't do that, it's too high Nathan. Lim won't send you the info you need either, you're wasting your time with him. There's a couple of other importers that use the same base unit but I'm buggered if I can remember the names. I'll do some searching and I'll come back to you.

[nathanjh13]

Thanks a million.

Yes I suspected so and as such I've not touched anything yet.

Shame he's so unhelpful. I guess he thinks his attitude is good for business.

Any help would be great here, I'm flying blind.

Thanks again
Nath

PS is it the Separo one here? Mind you it doesn't look like it underneath http://www.hifiandaudio.com/p88i.htm

[nathanjh13]

No prob, looking at the figures I'm going to set to 31.5 (avg) and that'll do. I'm sure I'll be within 5% of the optimum setting anyway.

Cheers
Nath

[nathanjh13]

Update: I use an OTL now and my old man inherited this. Even so, to anybody looking for an easy solution to biasing then I'd simply search ebay (worldwide) for:

Tube Amp Bias match Meter

and follow the instructions on screen.

Best
Nath