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Pye B16 Substitute frame output valve.

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Till Eulenspiegel
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The Mullard ECC34 double-triode is employed in the Pye B16 as the frame oscillator and output. This valve is becoming scarce and now that the audiophools regard the valve as something special when one does turn up for sale it is expensive. We know that the common 6SN7GT doesn't work well in the Pye B16, the 6N7 isn't suitable because it has a common cathode connection. Well now Forum member BrianC believes he has the answer, the American double-triode type 6DR7. This tube was developed specially for frame timebases. The first section has a low mu and is intended to function as the oscillator. The other section is altogether different being a big beefy device having a large grid base to handle a high sawtooth drive.
From the Radiomuseum: http://www.radiomuseum.org/tubes/tube_6dr7.html
The 6DR7 has a B9A base and the ECC34 has the international octal base so an adaptor will have to made.
And as you all know I like adaptors and adaptor plates so let's see what be done to solve the valve problem in the Pye B16. I've got two sets here to experiment on.
Size wise, the 6DR7 is about the same as the PCL84.

Till Eulenspiegel.

 
Posted : 06/06/2015 6:40 pm
DangerMan
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Another American valve "intended for the job" is 6BL7GT or even 6BL7GTA.

These are octal based and would appear to be very similar to ECC34 right down to the pin outs; the difference with the GTA version being that one section is specifically intended for use as the oscillator... which, ISTR is actually the one that Pye did use. The two sections are nominally the same but with some constructional differences to suit the "low current" side..
Perhaps this was 50:50 luck, but if I know Pye it could just as well have been deliberate.

I have obtained a couple of these which I haven't got round to trying yet, but perhaps I ought to. They don't yet seem to be as sought after as ECC34's, but audiophools are certainly aware of them 🙁

The heater is a rather greedier at 1.5A compared to 0.95A for the ECC34, but the extra half amp or so is a small-ish proportion of the set's total heater consumption.

Pete

 
Posted : 06/06/2015 9:01 pm
Till Eulenspiegel
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From the Radiomuseum: Info about the 6BL7GT http://www.radiomuseum.org/tubes/tube_6bl7gt.html Also, the circuit of a simple frame timebase. Linearity is adjusted by altering the bias of the amplifier section. Not nice.

Till Eulenspiegel.

T

 
Posted : 06/06/2015 9:30 pm
Till Eulenspiegel
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I knew I'd seen that valve before. The 6BL7GT was used as the frame output valve in the RCA CTC2B chassis, the model 21CT55. A colour set which was a development of the RCA CT100.

Till Eulenspiegel.

 
Posted : 06/06/2015 11:16 pm
DangerMan
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I've just tried them in my D16.

This set struggles for height anyway and has an oddball RS frame output transformer... I've tried a couple of ECC34's and they behave identically... I suspect the transformer could really do with being replaced which is why I've never bothered before.

Anyway, the 6BL7GT's work with no changes whatsoever to the circuit. In fact, they might even have a bit more height to offer, but they will only just lock with the frame hold pot right at the top end.
It appears that subject to a bit more checking (for correct anode current etc.) and possibly a tweak to the oscillator they would make a decent substitute. Apart from the frame hold, no adjustments were necessary.
They do not appear in any way distressed, and don't feel or smell hotter than the ECC34, so it's likely (considering the linearity etc. is correct) the anode current is somewhere near the correct value.

 
Posted : 07/06/2015 12:58 am
Brian Cuff
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I've ordered a couple of 6BL7GTAs from the US and I'll try one in my D16T. If it works, Till, the other one is for you.

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Posted : 10/06/2015 5:08 pm
Till Eulenspiegel
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Hi Brian,
If the 6BL7GT can deliver enough scanning power for a 70 degree colour tube operating at 23KV it'll be on easy street when it comes to the B16. 50 degree CRT operating with 5KV EHT.

Thanks for the offer of one. I look forward to trying it out in the Invicta T100. A D16 with minor cabinet details.

Till Eulenspiegel.

 
Posted : 10/06/2015 8:47 pm
Cathovisor
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One notable difference is that the 6BL7GTA uses 0.55A more heater current than the ECC34. Probably academic in a TV set, but worth noting.

 
Posted : 10/06/2015 9:14 pm
Studio263
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I've seen good results from the 6SN7 in a Pye 16, it is a good valve to pick as it looks right and doesn't involve too much messing about to fit. The trick is to optimise the value of the cathode resistor of the output half once the valve is fitted, an easy way to to wire a variable one in and adjust for the best height / linearity comprimise - a fixed resistor of the correct value can then be fitted. A friend of mine has a D16T which has been modified in this way and it gives ample height and solid lock. The 6SN7 used in that case was an old one, I don't know how the modification would work with the more modern sort which is indended for (less demanding) audio applications.

Of course it follows that the rest of the set needs to be in sound condition and the HT voltage up to the proper level for this method to work properly.

 
Posted : 15/06/2015 1:43 pm
Till Eulenspiegel
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The McMichael 512 got away with just using a 12AU7/ECC82 as the frame blocking oscillator and output. The Masteradio T852 uses the 6SN7GT in the same circuit configuration. Some later sets use the Mazda 6L1. The 6SN7 and the 12AU7 are very similar and I guess so is the rare Mazda 6L1.
These wee valves work well in the frame timebases of these small screen TVs. However, another early set, the Ekco TSC30 of 1946 employs a huge Mazda AC6PEN as the frame output valve.

Till Eulenspiegel.

 
Posted : 15/06/2015 4:34 pm
Studio263
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Screen shots of a D16T with a 6SN7 in it here:

http://www.vintage-radio.net/forum/show ... p?t=104768

 
Posted : 16/06/2015 1:12 pm
Brian Cuff
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I've just received the 6BL7GTAs from the states so will try them in my B16T next week and show some pictures. I know what will happen though - the set will have developed a fault and I'll have to fix it first :aa

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Posted : 21/06/2015 11:48 am
Till Eulenspiegel
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Both my D16 receivers have developed faults and that's the reason I have not posted up any info about frame valve substitution.
More glasnost: the truth is the D16 is a set I have never liked, in fact I think it is a horrid little thing. There are much better post-war sets about.

Till Eulenspiegel.

 
Posted : 21/06/2015 12:11 pm
Brian Cuff
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You might not like them Till, but the BBC used them in their control rooms as monitors so they must have had something going for them! I have a picture somewhere, of two of them used in an outside broadcast situation but I can't find it! They can give very good pictures.

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Posted : 21/06/2015 1:27 pm
Till Eulenspiegel
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Hi Brian,
There is no doubt the D16 displays a good picture, but for some reason it's a set I just don't enjoy working on. It's things like those dodgy slider controls and the EF50 valveholders. I'm not all that keen on the B18 LV20 series either.
There is a LV30 upstairs, reluctantly, I decided to do some work on it. I discovered that is it an excellent receiver. Pye TVs from 1950 are OK by me.

Till Eulenspiegel.

 
Posted : 21/06/2015 1:39 pm
Brian Cuff
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Here's a picture of three D16Ts in the BBCs Olympic control room in 1948. The OB van was parked at Wembley Stadium and the programs were directed from this control room with the vision mixer in the scanner responding to instructions from here.

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Posted : 21/06/2015 4:53 pm
mark pirate
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I'm not all that keen on the B18 LV20 series either.

I think these are great little sets, I restored my D18T that had been left in a loft for 50 odd years. It just needed recapping and a new EY51, it has had a lot of use since and proved to be very stable and has a great picture.

The same is true of the LV20, I much prefer working on these than a Bush TV22/24!

I bought a second D18T recently, it is a totally original and untouched set. I tacked in new smoothers and it came straight up with a good picture :aad

The set I really hate working on is the EMI 1807.... :-o

 
Posted : 22/06/2015 8:21 am
Till Eulenspiegel
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The set I really hate working on is the EMI 1807.... :-o

Standby for my next exciting project. I am going to prove that the HMV 1807 and Marconi VT53 was not a bad set after all and was genuine attempt by EMI to offer the buying public a new TV set at a reasonable price.

Till Eulenspiegel.

 
Posted : 22/06/2015 10:29 am
mark pirate
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Now that will be a Task :aak
My most difficult restoration to date was my Marconi VRC 74DA, the radio was a doddle (made by Plessey) but that awful 1807 chassis had more faults and problems than any TV I have encountered!
I am still struggling to get my HMV 2811 to give me more than 2kv of EHT, despite fitting another good LOPT :zx:

I wish you the best of luck David.

 
Posted : 23/06/2015 6:53 pm
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