HMV1902 - CRT Substitution, and restoration tips - UK Vintage Radio Repair and Restoration Discussion Forum

Sean Williams · 3rd Sep 2007, 10:56 pm

Well, I felt sorry for it, what with its decapitated tube, and unloved exterior...

Anyway, Seeing as a 15" round crt is likely to be rocking horse dung, is there any reason that I couldnt fit a rectangle tube? - The later model lists a 17" CRT....

Whilst we are at it, any pointers for this behemoth of a set?

Cheers

Sean, soon to be living in the set!

Steve_P · 3rd Sep 2007, 11:54 pm

This isn't the Radiogram Version of the HMV1901 / VT50E set with all it's problems is it? If so, you've taken on quite a repair job there. These sets generate one fault after another...!

What's the tube no inside it, and the 17 inch one you plan to fit? Then I can see what to do to make them fit.

Ready for the zillion queries....

Cheers,

Steve P.

Spell Room with an 'F'? Roof perhaps. Or being crude about it.... oh never mind.

Sean Williams · 4th Sep 2007, 7:46 am

Hi Steve,

Righto, the original tube is an EMISCOPE 3/6A - I have a quantity of Mazda CRM171 tubes here in stock....

Erm, the set looks identical to the 1901 autoradiogram on Jon's website - not sure if HMV made two similar sets in the same year?

The 3902 has a 17" crt....

Repairing this will be far easier than negotiating space for it to live in!

Duke_Nukem · 4th Sep 2007, 8:09 am

The 1902 was released ~1950 and whilst externally looks the same as teh much earlier 1901 I'd assume was much different to the 1901 internally (in fact I'd be suprised if it wasn't more similar to the 1805 range).

As for fitting a 17" rectangular tube, mechanically it would be easier (easier, not easy) than many sets as the tube doesn't mount on a chassis but has it's own support and lots of space around it.

What won't work though is finding enough scanning power. Also, although I don't have the data to hand, I suspect HMV might well have been continuing to use a comparatively feeble (volts-wise) mains EHT in which case you wont see much on your 17" tube !

I better option would be to look out for a round 15" Mazda tube [thinks : never thought I'd see myself recommending a Mazda CRT!]. If the original Emiscope can't be rebuilt (too damaged, or problematic glass type) then I'm sure if necessary the Mazda could be rebuilt. Not cheap, but the set must be very rare and worth keeping as original as possible. Certainly I'd wait a year and see ... you never know what might turn up.

TTFN,
Jon

Sean Williams · 4th Sep 2007, 8:22 pm

Piccy to follow when I get home from work at a sensible hour - the set is currently in my Garage - space for this beastie is going to be a challenge!

A 15" Mazda would be a good idea - will see what is about....

no real rush, lots to do here!

I guess service data is going to be as rare as the CRT!

Cheers
Sean

FERNSEH · 4th Sep 2007, 8:48 pm

The HMV 1902 TV chassis is similar to the 1806, the mains derived EHT is only 6KV. I doubt if any 17" 70 degree CRT would work in this range of receivers.
The minimum operational EHT for the Mullard MW43-64/69 is 10KV and I guess it's the same for the Mazda CRM171/2. The Mazda CRM151 might work but even this early tube requires 10KV.
The EHT could be boosted by using the pulse present at the anode of the KT44 line output valve and adding it to the 6KV supply, but then the scanning power will have to increased. It will be a big job converting this set to a more modern tube.
I have a 10" HMV 1805 and this set has a broken tube. I'm considering using the 10BP4 as a substitute.

DFWB.

Steve_P · 5th Sep 2007, 12:48 am

OK - Here's the info you probably don't want to read.

The EMISCOPE 3/6A Tube works on a low EHT - 4.0 kV to be exact. The ones you have expect a higher EHT Voltage.The EHT Voltage of the CRM171 is 16kV. This set uses Mains EHT at a guess, whereas 16kV is probably generated off the Line Stage.

One thing you could try is hooking a tripler (A BRC1500 5 Stick may do) on the Line Output Valve Anode. It may generate enough!

Or contact that bloke in France and see what he can do.

Cheers,

Steve P

Heatercathodeshort · 5th Sep 2007, 7:46 am

The official replacement for the 3/6A is the aluminised TA15 plus a modification kit supplied with the tube that boosted the EHt as David suggests. The kit also contained a new base and brackets etc. 15" tubes are difficult to obtain and the very low EHT potentials used by EMI make the situation more difficult. Surprisingly the pictures were of reasonable brightness. The 3/6A is a pre war tube. Regards, John.

Duke_Nukem · 5th Sep 2007, 8:17 am

Just a though, but how easy (or not) would it be to use the 10" tube instead ? No, not as a long term solution, but rather it would enable the rest of the set to be worked on whilst searching for a pucka tube. I guess if it were me I'd be reluctant to think of spending the money on rebuilding the tube whilst the rest of the set was a complete unknown.

Quote:

Originally Posted by Sean Williams

Hmm, not good - I see why the set was so cheap now!

If there weren't any other bidders (I only saw your bid) then you still have a _major_ bargain, to say nothing of a rare beast and part of me is quite jealous. Worth saving especially as the photos seemed to indicate the cabinet wasn't bad.

TTFN,
Jon

Sean Williams · 5th Sep 2007, 8:06 pm

Yes, only cost me £20.00, so I cant grumble - cheap, and a fantasticly imposing set - Piccys tomorrow I think.

I might well try a Radar tube for now - this might allow some sensible testing to occur.

Failing that, I could build a seperate EHT unit........

Cheers
Sean

ppppenguin · 5th Sep 2007, 8:20 pm

Quote:

Originally Posted by Sean Williams

Failing that, I could build a seperate EHT unit........

This is a worthwhile use for some bits from old 15" CRT computer monitors which you can't even give away on freecycle now.

Sean Williams · 6th Sep 2007, 4:27 pm

Well, I took a nose inside the set today - It has an EMISCOPE TA15, not sure if that is good news or not.....

It is very much shorter than it used to be - sadly the phosphor is also damaged, so I am unsure if a rebuild of the CRT is going to be viable.

A few piccys below

Sean Williams · 6th Sep 2007, 4:37 pm

Ok, well, while I look at the predicament of the tube, and take Jon's suggestion seriously - I have a few 7bp7 crts here still - I know it will over scan a tad, but is there any reason why I shouldnt give it a go?, I guess I need to think about the electrical stuff - I suppose the power unit would be the first thing to start with? - The Radio isnt really an issue - If I cant get that going then I really ought to give up!

I feel the need for service info! - any offers?

Steve_P · 6th Sep 2007, 6:10 pm

The TA15 had an EHT Multiplier of some kind - took it up to 7kV. Could I have pics of the Power Supply and Line Output stages?

Don't know about Service Data yet - will look. Have you got the info on the 7BP7 crt ?

Cheers,

Steve P

murphyv310 · 6th Sep 2007, 6:37 pm

Hi .
This may be silly but since I have been repairing pressure washers, most machines use a step up transformer that is quite compact that produces 11kv AC for the ignition in hot water machines.
My drift here is this 11KV 50HZ AC could be rectified for an EHT supply. The transformer's don't produce huge amounts of current so are much safer than the mains derived EHT found in earlier sets.
Trevor.

Sean Williams · 6th Sep 2007, 6:38 pm

Hi Steve,

Ok, will nip up the garage, and remove the chassis......

Piccys to follow

Sean Williams · 6th Sep 2007, 7:40 pm

As Requested!

A seriously heavy lump!

Duke_Nukem · 6th Sep 2007, 9:22 pm

Quote:

Originally Posted by Sean Williams

sadly the phosphor is also damaged, so I am unsure if a rebuild of the CRT is going to be viable.

I’m not sure if this will be a prob, as I believe the phosphor is replaced as part of the rebuild.

Quote:

Originally Posted by Steve_P

The TA15 had an EHT Multiplier of some kind - took it up to 7kV.

I wonder if the 1902 is similar circuit to the 2851? That too has a 15” TA15 and does not use any multiplier.

TTFN,
Jon

Ps : Data for 2851 is at http://www.thevalvepage.com/tvmanu/hmv/hmv.htm)

Steve_P · 6th Sep 2007, 9:45 pm

Looks similar.

But the EHT generated is higher for the TA15. I'd go off that and replace everything that looks as though it needs replacing. I don't know about the radio side, but that's the least of our worries!

Cheers,

Steve P.

(I'll check my paper stocks tomorrow. It's dark now!)

Sean Williams · 6th Sep 2007, 10:05 pm

Oh, 7bp7 specs.....

3rd Sep 2007, 10:56 pm	#1
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	HMV1902 - CRT Substitution, and restoration tips Well, I felt sorry for it, what with its decapitated tube, and unloved exterior... Anyway, Seeing as a 15" round crt is likely to be rocking horse dung, is there any reason that I couldnt fit a rectangle tube? - The later model lists a 17" CRT.... Whilst we are at it, any pointers for this behemoth of a set? Cheers Sean, soon to be living in the set! __________________ Engineers make things work and have spare bits when finished

3rd Sep 2007, 11:54 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: HMV1902 - CRT Substitution This isn't the Radiogram Version of the HMV1901 / VT50E set with all it's problems is it? If so, you've taken on quite a repair job there. These sets generate one fault after another...! What's the tube no inside it, and the 17 inch one you plan to fit? Then I can see what to do to make them fit. Ready for the zillion queries.... Cheers, Steve P. Spell Room with an 'F'? Roof perhaps. Or being crude about it.... oh never mind. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

4th Sep 2007, 7:46 am	#3
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: HMV1902 - CRT Substitution Hi Steve, Righto, the original tube is an EMISCOPE 3/6A - I have a quantity of Mazda CRM171 tubes here in stock.... Erm, the set looks identical to the 1901 autoradiogram on Jon's website - not sure if HMV made two similar sets in the same year? The 3902 has a 17" crt.... Repairing this will be far easier than negotiating space for it to live in! __________________ Engineers make things work and have spare bits when finished

4th Sep 2007, 8:09 am	#4
Duke_Nukem Octode Join Date: Jan 2003 Location: Birmingham, West Midlands, UK. Posts: 1,268	Re: HMV1902 - CRT Substitution The 1902 was released ~1950 and whilst externally looks the same as teh much earlier 1901 I'd assume was much different to the 1901 internally (in fact I'd be suprised if it wasn't more similar to the 1805 range). As for fitting a 17" rectangular tube, mechanically it would be easier (easier, not easy) than many sets as the tube doesn't mount on a chassis but has it's own support and lots of space around it. What won't work though is finding enough scanning power. Also, although I don't have the data to hand, I suspect HMV might well have been continuing to use a comparatively feeble (volts-wise) mains EHT in which case you wont see much on your 17" tube ! I better option would be to look out for a round 15" Mazda tube [thinks : never thought I'd see myself recommending a Mazda CRT!]. If the original Emiscope can't be rebuilt (too damaged, or problematic glass type) then I'm sure if necessary the Mazda could be rebuilt. Not cheap, but the set must be very rare and worth keeping as original as possible. Certainly I'd wait a year and see ... you never know what might turn up. TTFN, Jon

4th Sep 2007, 8:22 pm	#5
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: HMV1902 - CRT Substitution Piccy to follow when I get home from work at a sensible hour - the set is currently in my Garage - space for this beastie is going to be a challenge! A 15" Mazda would be a good idea - will see what is about.... no real rush, lots to do here! I guess service data is going to be as rare as the CRT! Cheers Sean __________________ Engineers make things work and have spare bits when finished

4th Sep 2007, 8:48 pm	#6
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: HMV1902 - CRT Substitution The HMV 1902 TV chassis is similar to the 1806, the mains derived EHT is only 6KV. I doubt if any 17" 70 degree CRT would work in this range of receivers. The minimum operational EHT for the Mullard MW43-64/69 is 10KV and I guess it's the same for the Mazda CRM171/2. The Mazda CRM151 might work but even this early tube requires 10KV. The EHT could be boosted by using the pulse present at the anode of the KT44 line output valve and adding it to the 6KV supply, but then the scanning power will have to increased. It will be a big job converting this set to a more modern tube. I have a 10" HMV 1805 and this set has a broken tube. I'm considering using the 10BP4 as a substitute. DFWB.

5th Sep 2007, 12:48 am	#7
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: HMV1902 - CRT Substitution OK - Here's the info you probably don't want to read. The EMISCOPE 3/6A Tube works on a low EHT - 4.0 kV to be exact. The ones you have expect a higher EHT Voltage.The EHT Voltage of the CRM171 is 16kV. This set uses Mains EHT at a guess, whereas 16kV is probably generated off the Line Stage. One thing you could try is hooking a tripler (A BRC1500 5 Stick may do) on the Line Output Valve Anode. It may generate enough! Or contact that bloke in France and see what he can do. Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

5th Sep 2007, 7:46 am	#8
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: HMV1902 - CRT Substitution The official replacement for the 3/6A is the aluminised TA15 plus a modification kit supplied with the tube that boosted the EHt as David suggests. The kit also contained a new base and brackets etc. 15" tubes are difficult to obtain and the very low EHT potentials used by EMI make the situation more difficult. Surprisingly the pictures were of reasonable brightness. The 3/6A is a pre war tube. Regards, John.

5th Sep 2007, 8:06 pm	#10
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: HMV1902 - CRT Substitution Yes, only cost me £20.00, so I cant grumble - cheap, and a fantasticly imposing set - Piccys tomorrow I think. I might well try a Radar tube for now - this might allow some sensible testing to occur. Failing that, I could build a seperate EHT unit........ Cheers Sean __________________ Engineers make things work and have spare bits when finished

6th Sep 2007, 4:27 pm	#12
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: HMV1902 - CRT Substitution Well, I took a nose inside the set today - It has an EMISCOPE TA15, not sure if that is good news or not..... It is very much shorter than it used to be - sadly the phosphor is also damaged, so I am unsure if a rebuild of the CRT is going to be viable. A few piccys below Attached Thumbnails __________________ Engineers make things work and have spare bits when finished

6th Sep 2007, 4:37 pm	#13
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: HMV1902 - CRT Substitution, and restoration tips Ok, well, while I look at the predicament of the tube, and take Jon's suggestion seriously - I have a few 7bp7 crts here still - I know it will over scan a tad, but is there any reason why I shouldnt give it a go?, I guess I need to think about the electrical stuff - I suppose the power unit would be the first thing to start with? - The Radio isnt really an issue - If I cant get that going then I really ought to give up! I feel the need for service info! - any offers? __________________ Engineers make things work and have spare bits when finished

6th Sep 2007, 6:10 pm	#14
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: HMV1902 - CRT Substitution, and restoration tips The TA15 had an EHT Multiplier of some kind - took it up to 7kV. Could I have pics of the Power Supply and Line Output stages? Don't know about Service Data yet - will look. Have you got the info on the 7BP7 crt ? Cheers, Steve P __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

6th Sep 2007, 6:37 pm	#15
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: HMV1902 - CRT Substitution, and restoration tips Hi . This may be silly but since I have been repairing pressure washers, most machines use a step up transformer that is quite compact that produces 11kv AC for the ignition in hot water machines. My drift here is this 11KV 50HZ AC could be rectified for an EHT supply. The transformer's don't produce huge amounts of current so are much safer than the mains derived EHT found in earlier sets. Trevor. __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

6th Sep 2007, 6:38 pm	#16
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: HMV1902 - CRT Substitution, and restoration tips Hi Steve, Ok, will nip up the garage, and remove the chassis...... Piccys to follow __________________ Engineers make things work and have spare bits when finished

6th Sep 2007, 7:40 pm	#17
Sean Williams Dekatron Join Date: Feb 2005 Location: St.Ippolyts, Hitchin, Hertfordshire QRA IO91UW Posts: 3,518	Re: HMV1902 - CRT Substitution, and restoration tips As Requested! A seriously heavy lump! Attached Thumbnails __________________ Engineers make things work and have spare bits when finished

6th Sep 2007, 9:45 pm	#19
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: HMV1902 - CRT Substitution, and restoration tips Looks similar. But the EHT generated is higher for the TA15. I'd go off that and replace everything that looks as though it needs replacing. I don't know about the radio side, but that's the least of our worries! Cheers, Steve P. (I'll check my paper stocks tomorrow. It's dark now!) __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?