Large Channel Imbalence KEL84

[mudvin]

Hi,

Yes I have swapped the source and the leads as well as the tubes from one side to the other, the issue remains in the Left Channel.

I do have a spare pot and will give it a try, however, as mentioned above it seems to test well.

Regarding the through hole plating, I meant that this particular PCB does not seem to have very good through hole plating, soldering one side the solder does not seem to reliably wick through to the other side like I am used to, and I have done several PCB projects

The other thing I had issues with were those PCB pins which kept wanting to fall out. However I have checked them all and they seem OK.

I will check that alternate pot, then I guess pull the PCB and look for anything out of the ordinary. The issue is that really I have already done that, so I probably need to pull some parts and check or replace them. The issue is which ones.

[BOONDI]

Do you have a scope?

I don't have a kel 84 here, so if it's not the pot, the two resistors into the grid or loose pin on the valves, im a bit stuck.

What i will do is pm this to one of the mods, who will prolly have avbetter diagram, or even a 84 sitting around.

Hth.

[mudvin]

Thanks very much for the help,

No no scope unfortunately.

In the meantime I shall try a new pot first, and then pull the PCB and check parts ( I may replace those resistors you mentioned just to see, even though they seem good).

I almost wish it was making loud crackling sounds, would be easier to track down, and I have never dealt with a push pull amp before, so the circuit is not particularly obvious to me. Pulling an replacing the PCB takes so long on this board it is a hassle to test individual components.

[BOONDI]

Hi Rob.

I sent a pm to a John Carswell. He's a supermod and he has more expertise than me with wd amps. It is 2am here so i would give it a bit till he sees my pm.

Try the pot anyways, you never know.

Without a scope it may be more difficult to track down. Hopefully it will be something glaringly obvious.

Derek.

[Richard]

Hi Rob and welcome,


Is this a new kit you've built yourself? Is it a power amp (single input) or integrated amp (multiple inputs). If integrated, what input selectors are used; rotary switch only or with electronic relays?

[mudvin]

Hi Richard

It is a new kit, Integrated amp with the relay board

I have tried replacing the potentiometer today with an alpha 50k I had lying around.

The issue still remains, although it is even more obvious (The pot is a lot less linear, may not be logarithmic). Basicly Right channel works as you would expect. Left channel sounds like it is not playing but if you turn the volume way up, it is and sounds clean, however the volume is maybe 1/8th or a 1/4 of the right channel.

[snowman_al]

Just wondering out loud here, but if the feedback loop is missing or a poor connection on the Right Hand channel, it will play much louder than the Left channel. Perhaps the problem is not on the left side?

Either do a continuity / resistance check round the right side R32 and the RFB wiring. Or as an experiment lift the feedback wire off the Left side and then see if it plays as loudly as the right.

I assume you have swapped speakers around.

[bob orbell]

Hi Mudvin, if you can post pictures of your build ( internal ) this my help us to see any issues. Bob

[mudvin]

Good Morning all,

We have progress, thanks snowman_al, I disconnected the feedback leads to both speakers and both channels went reduced volume, but the same level. Further pressing the appropriate feedback leads to the terminals brought the amp back to full volume on both channels.

It appears that the issue may be a bit of insulation on the resistor attached to the terminal, was insulating the feedback lead somehow. So a silly problem.

I have only tested the unit on old speakers, and the amp currently has an intermittent signal due to me messing up the input wires while moving the pot around). However I believe this could be the answer. Life calls so it will be a few hours, however I will give an update once the amp is back together and tested on better speakers.

Thanks everyone for the help so far, I will give an update either way if the problem comes back.

Rob

Originally Posted by snowman_al

Just wondering out loud here, but if the feedback loop is missing or a poor connection on the Right Hand channel, it will play much louder than the Left channel. Perhaps the problem is not on the left side?

[Richard]

Well done Rob and all that is good news!

Two things will happen with the connection/disconnection (or a poor connection) of the feedback wires at the black speaker posts (signal ground),

1) global feedback which will cause a lowering of volume when connected and operating

2) the cathode resistor 750R ground connection for the pentode first section of the ECF80 without which the pentode section will not operate (no volume).

What may have been happening sounds like a poor connection which may give an erratic mixture of those functions.

Best now to check and remake all the signal ground connections, in partic the fb wires and black speaker posts, back to signal ground on the pcb