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DHT matching in a SET amp
DHT matching in a SET amp
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Old 14th September 2018, 07:25 AM   #11
6A3sUMMER is offline 6A3sUMMER  United States
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tizman,

If you are going to use self bias, that will help you to do some reasonable matching.
If you can get a few 45 tubes you can just read the bias voltage of the two tubes and compare.
I do not know if there are amateur swap meets or antique radio swap meets in Toronto,
but if so, look for a few 45 tubes.
Sometimes even New Old Stock tubes can go gassy (I had one that went bad after not being used for (decades?), and re-activated for a few hours in one of my amps, then I turned it off. The next morning it was gassy and bad.

Take a couple that are close and then compare the gain of the two channels.
It does not have to be perfect, you can enjoy them if they are even close.

I would expect push pull might be a little more of a problem in regards to matching.
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Old 14th September 2018, 07:46 AM   #12
45 is offline 45  Italy
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Quote:
Originally Posted by tizman View Post
Thanks for the info 45. I donít have an operating 45 amp at the moment, although one is in the works, and I donít know anyone who has one either. Itís lonely in DHT land. Measured on an old Stark emissions only tester, I have several pairs that do match for emmissions, and the TJs that are perfectly matched in factory. Maybe I should sell off all the old 45s and buy a pair of EMLs?
As I said with the 45's it's rather easy to find matched tubes even using a single point tester because they are low mu with moderate gm.
I have two quads one RCA and one Raytheon that I will soon bring to UK and curve-trace. They measure almost identical with each quad on the Hickk but different from one quad to the other. It's the Raytheon that shows unusually higher gm at 2.35-2.4 mA/V. The RCA's measure as expected from new tubes at 2.2-2.25 mA/V. Will see how matched they are overall but from what I have seen in amplifiers it's not an issue at all.
The EMLs have now gained reliability which was not the case some years ago. The KR I don't know but it looks like the original also aesthetically.
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Old 14th September 2018, 09:57 AM   #13
tizman is offline tizman  Canada
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6A3sUMMER: it seems I should be okay given that I have a reasonable selection of 45s on hand, and I am running self bias.
45: what is it about the TJ Fullmusic/Sophia tubes that makes you say that they aren’t really 45s?
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Old 14th September 2018, 10:15 AM   #14
45 is offline 45  Italy
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Quote:
Originally Posted by tizman View Post
45: what is it about the TJ Fullmusic/Sophia tubes that makes you say that they arenít really 45s?
Those I could test from a friend of mine had more gm and gain. No a bad thing to have at all anyway. I didn't make that comment to dismiss them. The construction is 300-like or at least has been derived from that but it's just appearance.
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Old 14th September 2018, 04:47 PM   #15
tizman is offline tizman  Canada
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45: Do you recall how much more GM and gain they had?
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Old 14th September 2018, 04:56 PM   #16
tizman is offline tizman  Canada
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There is very little online with respect to reviews for the TJ 45/n.
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Old 14th September 2018, 06:21 PM   #17
45 is offline 45  Italy
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Originally Posted by tizman View Post
45: Do you recall how much more GM and gain they had?
About 2.6-2.7 mA/V and gain just over 4. Not a big difference but would be enough to classify it as not exact replica.
This was a few years ago. It was the one with black base and green printing. Things might have changed in the meantime.
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Old 14th September 2018, 07:46 PM   #18
tizman is offline tizman  Canada
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Thanks45. The tubes I have are the same as the ones you measured from a few years ago.
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Old 14th September 2018, 08:54 PM   #19
45 is offline 45  Italy
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Look here:

Sophia Electric's Home Page

If you go to the 45/n page there are curves and measured parameters. gm=3.2 mA/V and mu=4 at 250V/36mA. This also means lower plate resistance around 1260 R.

Maybe they can tell you more about typical values.

Last edited by 45; 14th September 2018 at 09:00 PM.
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Old 15th September 2018, 08:26 AM   #20
tizman is offline tizman  Canada
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Thanks for the link 45.
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