Hot tubes!

[Richard]

Hi Mark, Bob,

Yes looking at a picture attached I cannot see R47 2W Brown-Black-Black 10R resistor anywhere in this or other pics but do have a careful check round as there is quite a bit of non standard wiring there.

Looking at the Chassis earth post it appears that,

there’s a black wire from IEC earth to the chassis earth post directly connected with,
the Yellow/Green Mains TX screen,
the Yellow Mains TX 3.15-0-3.15 0V wire,
and a Black 0V wire which should go to the PSU Star Earth point.

I would,
remove the Yellow Mains TX 3.15-0-3.15 0V wire and the Black 0V wire which should go to the PSU Star Earth point from the post and reconnect them via a 10R resistor.

Then check with the multimeter that chassis is directly bonded to mains earth pin, and there is 10R between signal ground and mains earth pin.

If you’re not happy checking through and doing this have a word with a repairer

[Markpab66]

Thanks for that detailed reply, Richard! I will do as you say, whoever built this amp did a really good job, I'll have a look around when I examine the amp, I'll probably have to send for the correct resistor tho. I should be OK repairing it, I recently built an amp kit from Douk audio - the 13w one with magic eye tubes. They didn't let on that the build manual isn't available in English anymore - just Chinese! Thank god for Google Translate! I'll keep you updated how I get on.

[bob orbell]

Hi Richard / Mark, my instructions say, from the star earth, a lead to R47 the resistor soldered to the earth post, the yellow wire, C/T from 6.3 heater winding, direct to earth post. Hope this helps. To be honest, if this was mine, I would remove all the add on bits and return to original. Bob

[Markpab66]

The builder of this amp put 2 switches on the side, to swap speaker terminals, I thought about removing these, thinking it was something to do with the hum. Also, it has 3 chrome knobs on the front, the center one is a 3 position tape monitor switch for 2 tape decks. It has numerous RCA inputs on the back including 3 auxiliary, 2 tape, a tuner and CD. I've ordered some 2 watt resistors, didn't want to start paralleling 1/4 watt ones, there's enough wires as it is in there!

[Richard]

Originally Posted by bob orbell

Hi Richard / Mark, my instructions say, from the star earth, a lead to R47 the resistor soldered to the earth post, the yellow wire, C/T from 6.3 heater winding, direct to earth post. Hope this helps. To be honest, if this was mine, I would remove all the add on bits and return to original. Bob

Hi Bob, yes I looked through and it was ambiguous but seems clearer on the circuit drawing attached

[Richard]

Originally Posted by Markpab66

The builder of this amp put 2 switches on the side, to swap speaker terminals, I thought about removing these, thinking it was something to do with the hum. Also, it has 3 chrome knobs on the front, the center one is a 3 position tape monitor switch for 2 tape decks. It has numerous RCA inputs on the back including 3 auxiliary, 2 tape, a tuner and CD. I've ordered some 2 watt resistors, didn't want to start paralleling 1/4 watt ones, there's enough wires as it is in there!

Hi Mark, yes it has quite comprehensive switching options presumably the builder was a tape enthusiast and needed to listen to each channel separately.

[Markpab66]

I know this is a silly question, but where is the star ground on this amp? I took a load of pics soon after I got this amp, and looking at them I can't seem to see a common grounding point, except for the one on the back panel where they are all attached now.

[Richard]

It's the tags where the White Mains TX and thick Black lead join in this pic. You'll see the white lead shown on the circuit diagram in the earlier post. The Mains TX yellow should also go there.


Do you have the circuit and build sheet pdfs (if not I can send)?

[Markpab66]

I see! Thanks for that. No, I don't have any build PDF's, would be great if you could send them to me. Thanks.

[Richard]

Hi Mark,

Pdfs sent.

R47 10R is not shown in the circuit in Kit34i or the parts list in Kit34in but is shown in KitKat34crt enclosed taken from the later amplifier-only version (but again not in the parts list). This may be why the builder of yours did not include it. It may have been missed from the drawing or a later addition to fix hum.

Bear in mind too that these drawings and kits were sometimes updated so the version I have may not be the same as another.

Rich