Hiwatt 200 Bias question

[ken]

Hello...

I'm working on a 1970's Hiwatt 200 with 4 KT88's.

I'm not getting enough bias voltage to the power tubes, even though I replaced the bias power cap, diode, and all four coupling caps. I'm told that low bias
voltage was the main cause of death in these amps.

Is there an easy way to put in a voltage doubler in the bias section?

Thank you,
ken

[Albert Kreuzer]

Here's a link to Mark Huss' Hiwatt page:

http://mhuss.com/Hiwatt/Schematics/BiasCkts2.gif

And attached there is a drawing Rick Erickson posted a while ago for a layout.

Hope this helps.

Cheers,
Albert

[Rob Mercure]

Ken,

I assume by now that you're aware that this is a very common problem with HiWatts and you're not alone in having to add doublers to these.

Rob

[ken]

I know...

I'm trying to make a doubler work with this amp, but there are "issues".
B+ at the power tubes is almost 700vdc, but the unmodded bias supply only put out -32vdc tops. The doubler I got from the GT Tube Amp Book makes way too much bias voltage, almost -80vdc at 110VAC input.

I'm told this will be this amp's third OT, and no wonder why.

Thank you,
Ken

[ken]

I just wanted to say Thank You for all the advice on the Hiwatt 200 (DR 201)'s bias issues. It works very well now indeed.

Now, I have a different problem with it. When I take the amp out of standby, it 'pops' loud enough through the speakers to make me worry about blowing them.

I changed the 220K bleeder resistors on the power capacitors and the standby switch, but it didn't help. Is there some mod I can do to this amp to remove the pop?

Thank you,
ken

[Dave Curtis, dB AudioTech]

I just wanted to say Thank You for all the advice on the Hiwatt 200 (DR 201)'s bias issues. It works very well now indeed.

Now, I have a different problem with it. When I take the amp out of standby, it 'pops' loud enough through the speakers to make me worry about blowing them.

I changed the 220K bleeder resistors on the power capacitors and the standby switch, but it didn't help. Is there some mod I can do to this amp to remove the pop?

Thank you,
ken

Does it do this with the volume down?