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 Valve defect
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 Return to top of page · Post #: 1 · Written at 11:32:52 PM on 6 April 2020.
Vintage Pete's avatar
 Location: Albury, NSW
 Member since 1 May 2016
 Member #: 1919
 Postcount: 1993

I have working valve I took out of a good working set and put it in a set that had issues.
The Valve is a 6cm5 and it works fine in both sets , but I noticed the glass has a defect in it like a indentation that causes the connection ontop of the valve to sit crooked and I wanted to ask is this a manufacturing fault or something else that can cause the glass to change shape slightly.
The Valve does work fine though.
Off set is probably a better term to use,the connection is off set due to a bend in the glass
Pete


 
 Return to top of page · Post #: 2 · Written at 12:16:51 AM on 7 April 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4345

I have quite a few of them. The only thing that usually goes wrong up top is the top cap breaking free.

If it works, no stress. I assume you know TC is the plate.


 
 Return to top of page · Post #: 3 · Written at 12:28:16 AM on 7 April 2020.
Vintage Pete's avatar
 Location: Albury, NSW
 Member since 1 May 2016
 Member #: 1919
 Postcount: 1993

Hi marcc,
Yeah the cap is fine, not loose and so is the valve,just a bend in the glass .must be from the manufacturer

Pete


 
 Return to top of page · Post #: 4 · Written at 10:21:30 AM on 7 April 2020.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1380

I once found a 6DQ6 line output valve that had gotten so hot that the glass had melted into a cocoon around the valve elements. The vacuum still appeared intact, but I had no way of testing it at the time.


 
 Return to top of page · Post #: 5 · Written at 11:47:20 AM on 7 April 2020.
Vintage Pete's avatar
 Location: Albury, NSW
 Member since 1 May 2016
 Member #: 1919
 Postcount: 1993

This one is only slightly dinged Robbert,but as I said it works fine ,just I've never seen that before.

Pete


 
 Return to top of page · Post #: 6 · Written at 12:08:37 PM on 8 April 2020.
Irext's avatar
 Location: Werribee South, VIC
 Member since 30 September 2016
 Member #: 1981
 Postcount: 400

I have seen valves that were misshapen after red plating for an extended time.
It seems the glass gets so hot that the vacuum sucks it in slightly.
A 6CM5 will red plate if the Hor drive is removed but usually are dead after this happens.


 
 Return to top of page · Post #: 7 · Written at 12:21:00 PM on 8 April 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1910

Yes a 6CM5 won't tolerate that kind of abuse for very long.
A 6CM5 was designed to work as a switch, which is why they make very bad audio amplifiers and why, deprived of drive and bias, they turn on so hard they destroy themselves quite quickly.

Pete your Pedigree has a little delay fuse in the screen circuit to protect against this. It's a half-watt resistor with a spring around it. Overload heats the spring, melts the solder and it pops open. Protects against loss of drive as well as damage to the screen grid if the 6AL3 fails, which they did, often. Also protects the hor OP transformer.


 
 Return to top of page · Post #: 8 · Written at 1:37:26 PM on 8 April 2020.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4345

One of the things that can happen is a failure in a power supply that is feeding the grid bias. Then we have diodes & things get seriously hot.


 
 Return to top of page · Post #: 9 · Written at 5:45:52 PM on 8 April 2020.
Vintage Pete's avatar
 Location: Albury, NSW
 Member since 1 May 2016
 Member #: 1919
 Postcount: 1993

Ian, this 6CM5 is not out of the Pye set,it's in one of my old 50s sets ,but the set runs/


 
 Return to top of page · Post #: 10 · Written at 10:01:38 AM on 9 April 2020.
Irext's avatar
 Location: Werribee South, VIC
 Member since 30 September 2016
 Member #: 1981
 Postcount: 400

What brand is the 6CM5?
I'll bet it's not a Trigon.


 
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