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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 21st Sep 2019, 2:18 pm   #61
turretslug
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Default Re: Alternative EHT system for HMV 902.

Being pedantic, I reckon the second-from-left "Philips focus resistor" in Argus 25's post# 57 is more like a VR68 than a VR37- VR37s are slightly smaller than the second-from-right "2W metal film" type. Surprisingly small considering their voltage capability but they evidently do their job, and VR25s are very small indeed, similar in size and style to Philips 0.25W carbon film types but with a pale blue finish and the non-metallic white or yellow tolerance bands. Things like Philips 'scopes abound with VR25s and VR37s but the much higher voltage rating VR68s are less widespread.
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Old 22nd Sep 2019, 5:26 pm   #62
beery
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Default Re: Alternative EHT system for HMV 902.

Quote:
Originally Posted by peter_scott View Post
Below is the original type of dog bones used in my focus chain. I think recreating these with modern components is rather difficult.

Peter
Hi Peter. That's a good photo of the cast end type of resistors I was trying to describe. I think they are unique to EMI. Their tag strips are another oddity, my research found out that they have German origins.

Cheers
Andy
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Old 22nd Sep 2019, 5:34 pm   #63
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Default Re: Alternative EHT system for HMV 902.

Hi Andy,

I stole the photo from an Atwater Kent forum. Unfortunately They aren't using any 500k ones in AK radios. The one on the left has actually been wire wound to create a "replica" but I would think it might be difficult to get enough wire on for our values.

Peter
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Old 22nd Sep 2019, 6:56 pm   #64
peter_scott
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Default Re: Alternative EHT system for HMV 902.

I found an American advert but perhaps there is more than one maker of this style.

Peter
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Old 22nd Sep 2019, 9:07 pm   #65
peter_scott
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Default Re: Alternative EHT system for HMV 902.

Aha! A British supplier. This looks like what was fitted to the EMI sets.
Wireless Magazine July 1935 page 469.

Peter
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Last edited by peter_scott; 22nd Sep 2019 at 9:12 pm.
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Old 24th Sep 2019, 6:48 pm   #66
FERNSEH
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Default Re: Alternative EHT system for HMV 902.

The CRT is reinstalled in the cabinet and the next task is to refit the timebase unit. That done we'll find out if the EHT transformer removed from the 902 works in this set.

DFWB.
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Old 24th Sep 2019, 11:18 pm   #67
FERNSEH
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Default Re: Alternative EHT system for HMV 902.

Tube had to come out again. The timebase unit should be installed before the CRT goes in.
That's been done so it's time to connect everything up again.

DFWB.
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Old 28th Sep 2019, 11:00 pm   #68
FERNSEH
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Default Re: Alternative EHT system for HMV 902.

After the installation of all the units it was time to test the replacement EHT transformer in the HMV 901. For the initial tests the two U14 HT rectifier valves were not fitted. 5KV EHT is present but the CRT heater is not lit. The tube heater checks OK but there is no 4volts present at the heater connections.
The power unit has to come out again which means removing the CRT.
So it's out with the tube again but it is possible to remove the power unit without taking out the timebase and receiver units. See attachment.
CRT heater supply fault turned out be a bad solder connection. That's fixed so the power supply and the CRT will be refitted.

DFWB.
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