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Old 17th Feb 2021, 12:15 am   #1
Helder Crespo
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Default Bush TV22 Mk 1 and 3/4

Some time ago I posted a thread on my second Bush TV22 (still waiting to be restored) with serial no. 124/06297 and RF deck A22/22715: https://www.vintage-radio.net/forum/...d.php?t=167087
In this set, everything points to an Mk2 (both the serial number and the main chassis' circuit and components), but the RF deck is populated with EF91 valves (even though it has a typical Mk2 s/n). Right now there's (yet) another TV22 on eBay with a reasonably close s/n (124/07010) and similar characteristics, including EF91s on the RF deck. No big deal, but it shows that at least some early Mk2s indeed had RF chassis with EF91s, contrarily to what is stated on the trader sheet.
https://www.ebay.co.uk/itm/BUSH-TV22...AAAOSwGXNgJrDl
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Old 17th Feb 2021, 8:43 am   #2
Ed_Dinning
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Default Re: Bush TV22 Mk 1 and 3/4

I think Bush were not too good at stock control/ ordering. I've seen DAC90a radios where the octal valve holes had been "plated" to allow a B8A base to be fitted

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Old 17th Feb 2021, 9:12 am   #3
Helder Crespo
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Default Re: Bush TV22 Mk 1 and 3/4

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Originally Posted by Ed_Dinning View Post
I think Bush were not too good at stock control/ ordering. I've seen DAC90a radios where the octal valve holes had been "plated" to allow a B8A base to be fitted

Ed
Thanks Ed. The RF deck on my set indeed seems to have been "plated" to allow fitting B7G bases for the EF91s.
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Old 17th Feb 2021, 9:52 am   #4
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Default Re: Bush TV22 Mk 1 and 3/4

In short: at least some early(ish) Mk2s had a true Mk2 main chassis but with an Mk1 RF circuit based on EF91s installed on an adapted (A22) Mk2 RF chassis. Bush possibly wanted to use their remaining stock of EF91s. Either that or they ran out of EF80s sometime along production.
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Old 28th Feb 2021, 12:07 pm   #5
Helder Crespo
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Default Re: Bush TV22 Mk 1 and 3/4

I wonder how many of these "hybrid" TV22 are out there. It would be great to hear from other forum members. The one on eBay that I mention on post #1 has recently sold for 225.01...
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Old 28th Feb 2021, 4:12 pm   #6
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Default Re: Bush TV22 Mk 1 and 3/4

It is not surprising that later versions of the TV22 employ EF91 valves. The later receivers types TUG 26,TUG34, TUG34A and TUG36, the later being one of the first to incorporate band 3, all sport EF91 valves. They perform just as good as the B9A EF80 and were probably a lot cheaper to buy in considerable bulk from Mullard.

Strangely the unscreened EF91 is not provided with an external screening can as is the norm with most receiver chassis. The EF80 is internally screened. The overall gain of the TV22 is fair for what it is but any extra stages of I.F. amplification may have created an instability problem. The EF91 is an incredibly good valve and was used as an audio output valve in a couple of makers chassis with very good results. J.
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Old 28th Feb 2021, 5:38 pm   #7
Helder Crespo
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Default Re: Bush TV22 Mk 1 and 3/4

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Originally Posted by Heatercathodeshort View Post
It is not surprising that later versions of the TV22 employ EF91 valves. The later receivers types TUG 26,TUG34, TUG34A and TUG36, the later being one of the first to incorporate band 3, all sport EF91 valves. They perform just as good as the B9A EF80 and were probably a lot cheaper to buy in considerable bulk from Mullard.

Strangely the unscreened EF91 is not provided with an external screening can as is the norm with most receiver chassis. The EF80 is internally screened. The overall gain of the TV22 is fair for what it is but any extra stages of I.F. amplification may have created an instability problem. The EF91 is an incredibly good valve and was used as an audio output valve in a couple of makers chassis with very good results. J.
Thanks John. Yes, that makes sense. The EF91 has better high-frequency response too, although I don't think this is very relevant for the TV22. The issue I raised was the fact that Bush already had their A22 RF decks designed and ready for EF80s, which required extra work at the factory ("plating") in order to install Mk1 circuits with EF91s on them.
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