KiT6550 distortion and voltages off - any ideas please?

[jdd308]

Hi all,

Hope you're all well and staying safe. It does mean we're all listening to more music which is great.

Until problems crop up. At the end a long (9-hour) session the other day I heard distortion on the left channel, so the next morning the cover came off and I found R38 was no longer attached to the valve base!

That must be it, so I checked it was still about 560 ohms on the meter, all good so repaired the joint and then tested voltages.

This left channel came out fine and quite close to what I normally get.

However, testing the right channel, which sounds fine, had no broken joints, and voltages are a different story.

Some are outside the 15% tolerance, although my mains voltage seems about 10% down.

Any thoughts? V3 and V4 are the really nice tall Telefunken E80CF – shall I swap them over and retest? I have a spare set and could test with these as well.

V3 pin1 should be 125vdc, tested 103v
V3 pin 2 should be 0v, tested 0v
V3 pin 3 should be 95v tested 62v
V3 pin 6 should be 130v tested 131v
V3 pin 7 should be 1.6v, tested 1.38v
V3 pin 8 should be 6.5v, tested at 6.4v

Thank you in advance for any help – the amp is quite old now, first built in 2004 and the last tinkering I did was in 2017 to turn it back in to an integrated amp.

John

[jdd308]

Just browsed the FAQs and seen John's post on ECF80 voltages for another amp - same is true here perhaps?

[bob orbell]

The ECF80 and its counterpart valves are renowned for big voltage fluctuations, don't worry. Bob

[jdd308]

Splendid thank you Bob, that's most encouraging...

[Phil Y]

Hello John,

For peace of mind, you could swap the ECF80s over and see if the voltages follow the valve, (which they probably will)

Phil.

[Richard]

John, what you didn't say was if re-soldering the resistor fixed the distortion and if it sounds fine again now.
If so the voltages have probably been a little "off" all along.
By all means swap valves and test the voltages again but the only valves which usually come somewhere near are Mullards. Not that it matters much so long as it sounds good.

[jdd308]

Hi Richard and thank you, good to hear from you. Yes the distortion is all cured, I am now listening to some lovely smooth music and all sounds fine.

I swapped the valves over and sure enough the voltages followed.

Thank you again for all your help it's not the first time you've all been so responsive, always a pleasure popping in here.

John