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Old 20th Nov 2021, 1:57 pm   #1
FERNSEH
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Default 6BX7GT as frame output valve in Pye B16T

The Pye B16T employs the the Mullard ECC34 as the frame oscillator and output valve. It's a valve that's becoming difficult to find.
Just arrived today a Sylvania 6BX7GT double-triode which was specifically designed for frame timebase work.
From the Radiomuseum: https://www.radiomuseum.org/tubes/tube_6bx7gt.html

Later today I'll try out the valve in the Invicta version of the B16T.

DFWB.
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Old 20th Nov 2021, 4:47 pm   #2
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Default Re: 6BX7GT as frame output valve in Pye B16T

The 6BX7GT has been fitted in the Invicta TL100 and the results prove the American valve is a satisfactory replacement for the ECC34 in it's application as a frame oscillator and output valve in the Pye B16T.
In the past a 6SN7GT has been tried in the set but the results weren't good.
Seemed the output section of the valve couldn't handle the sawtooth waveform applied to the control grid.

DFWB.
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Old 21st Nov 2021, 1:02 pm   #3
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Default Re: 6BX7GT as frame output valve in Pye B16T

Interesting David. It makes a very good replacement for the ECC34. Fortunately the ECC34 are very good valves and seldom fail in the B/D16T. The 6BXtGT may be as difficult to obtain as the ECC34 but probably a lot cheaper. John.
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Old 28th Nov 2021, 1:17 pm   #4
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Default Re: 6BX7GT as frame output valve in Pye B16T

What about a 12BH7 in an adaptor? Wired of course for 6.3v.
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Old 28th Nov 2021, 4:24 pm   #5
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Default Re: 6BX7GT as frame output valve in Pye B16T

Hi Trevor,
never tried tried the 12BH7 in a B16T. The valve was used as a frame oscillator and output with success in many Masteradio TV sets including 21" models TE21C and TF21T.
An interesting alternative to the ECC34 is the American 6BL7GT. Pin out is the same as the ECC34. Both triodes sections in the 6BL7 have identical characteristics? Confirmation required.
From the Radiomuseum: https://www.radiomuseum.org/tubes/tube_6bl7gt.html
The 6BL7GT was used as the frame oscillator and output in the CBS 205 colour TV receiver so it should be up to the job in a 9" TV receiver with only 5KV EHT.
Another valve I haven't tried in the B16T is the American 6DR7. Again, a valve designed as the frame oscillator and output in TV receivers.
The triode sections have different characteristics. B9A base.
https://www.radiomuseum.org/tubes/tube_6dr7.html

DFWB.
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Old 2nd Dec 2021, 11:23 pm   #6
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Default Re: 6BX7GT as frame output valve in Pye B16T

Hi
A 6BX7GT has been fitted to a B16T belonging to a local enthusiast and he says after an hours running height slowly drops with a little frame cramp at the bottom. The circuitry has been checked with no apparent issues.
I'm wondering if its either a faulty valve or its not up to the requirements of the B16T?
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Old 2nd Dec 2021, 11:32 pm   #7
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Default Re: 6BX7GT as frame output valve in Pye B16T

Hi Trevor,
I'm sure the 6BX7GT should be up to the task as a frame oscillator and output valve in a B16T. The valve was used in many American TV sets of the same era.
Don't think 50Hz operation instead of 60Hz should make any difference.

DFWB.
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Old 4th Dec 2021, 11:49 pm   #8
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Default Re: 6BX7GT as frame output valve in Pye B16T

Arrived today a 6BL7GT double-triode.
The 6BL7GT is a valve designed for frame timebase use in 525 line TV receivers.
Tried out the valve in the Invicta TV set. Good results, gives more spare height than the ECC34 and 6BX7GT double-triodes. Pin for pin compatible with the ECC34 and 6SN7GT.
The section connected to pins 1, 2 and 3 is optimised for service as the output valve which is OK in the B16T and the Invicta T100 because that's how the valveholder is wired up in these receivers
No improvement with the frame hold though, the hold control still needs constant resetting.

The 6BX7GT performed almost in the same manner as the ECC34. That is, a reduction of picture height after two hours.

DFWB.
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