Re: Question and comment on tube matching

Posted by Legendre (A) on April 11, 2006 at 16:02:26

In Reply to: Question and comment on tube matching posted by Lew on April 11, 2006 at 10:04:48:

Lew,

FWIW - the two matched quads which I received from New Sensor seemed *very* well matched, at least in terms of DC. When setting up the amps, I set a nominal bias voltage with the control, and used a voltmeter across the two grid busses to set them perfectly even, with the DC offset control.

When I plugged in the tubes and ran it, there was almost zero DC offset in either chassis.. Just a few mA on the meter. Basically, I fed them even grid voltages, and they responded evenly. That was a very good sign, and a great relief.

One problem with matching the 6C33 tubes stems from their thermal acceleration (might call it runaway) tendencies. The tubes must be run and held near full bias for several hours, so that these tendencies can manifest - and then matched groups are selected based on final 'hot' current readings. I'm not exactly sure how Otto's matching rig works, but he did mention that it was custom built just for the needs of the 6C33.

One other thing I observed, and it may relate to the thermal characteristics. When the tubes are left in standby, the cathodes run at a particular color (orange, of course) and stay there. However, once they are biased up and allowed to get hot, I believe that I saw the cathodes glowing more brightly.. My theory is that a substantial amount of the heat dissipated in the plate is returning to the cathode as IR, causing it to run hotter (and glow more brightly) thus increasing the emission, and thus the tendency to run away. Much like bumping up the filament voltage on a tube tester will cause most tubes to read higher.

Have you ever observed this on your MA-240s? It's just a theory, and I'm not certain about it.. but it does seem to explain the behaviour.

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Follow Ups Full Thread

Topic - 6C33C-B & Novacron revisited - Legendre 16:50:26 04/05/06 (23)

MA240SE - Lew 08:39:04 04/10/06 (0)

Re: 6C33C-B & Novacron revisited - 6C33DG 19:01:26 04/09/06 (0)

any other Novacron photos available besides the usual Atma-Sphere pic? - Bersani 22:31:02 04/06/06 (14)

Not the greatest pic, but.... - Sue Kraft 13:46:10 04/07/06 (13)

Cool, thank you (and lucky you, as well)! (nt) - Bersani 17:49:59 04/07/06 (0)

Now who built those? - Legendre 16:01:02 04/07/06 (11)

Would you believe I did? - Sue Kraft 20:17:04 04/07/06 (10)

that explains why the output tubes are installed backwards. - lone gunmen 05:34:37 04/08/06 (9)

No wonder... - Sue Kraft 07:13:05 04/08/06 (8)

madam,you're a dumb-sh*t. - lone gunmen 13:17:26 04/08/06 (7)

Jeez.... - Mike Currie 12:55:37 04/11/06 (0)

Way uncalled for - BlackPlasticSound 22:52:11 04/08/06 (1)

I agree it was uncalled for - MIchael Samra 09:40:27 04/10/06 (0)

Now I understand why the OTL board is so dead most of the time - Sue Kraft 16:04:25 04/08/06 (3)

Not Defending the Gunslingers, but... - LineArrayNut 01:14:51 04/10/06 (1)

Re: Not Defending the Gunslingers, but... - Legendre 07:27:11 04/10/06 (0)

Thanks anyway Sue. Unfortuntely some people lack basic social skills. (nt) - Bersani 23:38:58 04/08/06 (0)

Re: 6C33C-B & Novacron revisited - chris keating 08:56:32 04/06/06 (0)

Re: 6C33C-B & Novacron revisited - morricab 04:21:45 04/06/06 (4)

Question and comment on tube matching - Lew 10:04:48 04/11/06 (3)

Re: Question and comment on tube matching - morricab 02:08:21 04/12/06 (0)

Re: Question and comment on tube matching - Legendre 16:02:26 04/11/06 (1)

Re: Question and comment on tube matching - Lew 09:01:58 04/12/06 (0)

Follow Ups

Re: Question and comment on tube matching - Legendre 16:02:26 04/11/06 (1)

Re: Question and comment on tube matching - Lew 09:01:58 04/12/06 (0)

Re: Question and comment on tube matching

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