KiT 6550 ECF 80 Pin 6 Voltage

[TimN]

I've just been tinkering with my 6550 fitting some new caps C7/8, C11/12/13/14 (Soniqs SAX) and on testing voltage on completion the voltages at Pin 6 on V3/V4 are out of tolerance, V3 above and V4 below.

V3 is 155.4V and V4 is 109.8V. Tolerance range is 110V-149.5V.

All other voltages seem OK.

Does anybody have any ideas why this might be?

Is it important?

I've only managed a short listen to it so far, but it seems OK beyond the new caps aren't burnt in yet.

[bob orbell]

Hi Tim, it has been said on here before about the ECF80 being way diferent from valve to valve, I don't think you have problem but hope someone ells like John will coment. Bob

[Mark]

Originally Posted by TimN

I've just been tinkering with my 6550 fitting some new caps C7/8, C11/12/13/14 (Soniqs SAX) and on testing voltage on completion the voltages at Pin 6 on V3/V4 are out of tolerance, V3 above and V4 below.

V3 is 155.4V and V4 is 109.8V. Tolerance range is 110V-149.5V.

All other voltages seem OK.

Does anybody have any ideas why this might be?

Is it important?

I've only managed a short listen to it so far, but it seems OK beyond the new caps aren't burnt in yet.

Tim,

I built a KEL84 around 20 years ago and was very alarmed by the ECF80 voltages being way out of tolerance. I am a Chartered Engineer so when something's out of tolerance it's not working properly ! (Dr) John Caswell on this forum checked out the amp for me and gave it a clean bill of health. IIRC there is a sticky about this somewhere on the forum. The ECF80 valves supplied with the amp were EI, which I also found to be a bit too microphonic for my room. I now use NOS Mullards. I don't know if some brands of ECF80 produce better or worse readings, but John assured me everything was OK after checking it out, and it's still playing fine as I type.

Mark

[Greg.]

I think this from John is what Mark refers to.

http://forum.world-designs.co.uk/showthread.php?t=3203

[TimN]

Thank you all very much. It's actually got some Mullard E80CFs in it, but it seems the issue is across both makes and types. It's like valves have minds of their own!

Tim

[Richard]

Tim,
I had the sister amp Kit34 and have had 2 Kel84s here for repair and didn't have a problem.
Whilst I'm sure the notes about makes of valves will be correct it may not be your reason.
So I'd do the normal checks yourself starting with swapping them L to R and re-checking voltages to see if it is the valves or the amp

[TimN]

Thanks Richard,

After I listened to it a bit more, there was an annoying low level buzz from the speakers and noisy volume pot. I'm going to rebuild the B9a sockets and fit a new ALPS pot with remote control and see if that sorts it.

I wish I'd left it alone now! It was working fine!

[bob orbell]

Tim, I had an issue with my KAT6550 years ago, it was standard trim and I never had any thoughts of changing any capacitors, I still do not subscibe to these fancy capacitors as do a few on here, but, I had a small hum from the word go and joined the forum for help, I was told that the value of C5 (120uF 500volt) had been reduced to 82uF, I did this and the hum was no longer presant, not saying this is your problem, but . As for burning in . Bob

[TimN]

Thanks Bob,

I've already dropped C5 to 100uF but I might try further as you suggest.

However, it's a buzzing rather than a humming that gets louder with the volume. I think it might be an earth issue. Maybe a whisker somewhere. I'm hoping it might resolve by rewiring the shielded cable around the B9a sockets and volume pot. I was tinkering around there when I fitted the relay board

Also, I've just noticed one of the phono socket earth tabs was touching the case wall.

Tim

[John Caswell]

Hi Tim,
If it gets louder as the volume is turned up, I suggest it is something to do with earthing around the relay board or the v/c. Also make sure that the input wiring is not near any mains or heater wiring.

John