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HMV1117 output valve

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Westcliff
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A colleague has asked me to take a look at his great aunt's HMV 1117, which he found in his loft the other day.

When I took the back off the first thing I noticed was a 6V6GT in place of the KT61. Is this an acceptable substitute?

Thanks.

Gus.

 
Posted : 04/09/2013 10:18 pm
Anonymous
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Hi Gus, the radio museum guys say that it is an ok replacement,
But the cathode resistor should be changed from 90 ohms to 270 ohms (1 watt)
Read the full storey here.
http://www.radiomuseum.org/tubes/tube_kt61.html

 
Posted : 04/09/2013 11:32 pm
Westcliff
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Thanks Rabbitstew, that link saved me from making a mistake (I thought KT61 and EL33 were the same).

That 6V6GT has to go and I hope I have a KT61 in my stash.

Gus.

 
Posted : 05/09/2013 1:53 am
turretslug
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That 6V6GT has to go

Gus.

But only into the valve stash! It's one of the all-time popular small output valves, with economical heater for its size (at least for indirect heater). And it'll only gain in value,

Colin.

 
Posted : 05/09/2013 3:27 pm
Anonymous
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Hi Gus
In case you were not aware of it, this site is also good for looking up valve data and equivelents.
http://www.r-type.org/search.php

and this site is good for looking up transistor data and equivalents.
http://alltransistors.com/

If you get stuck I think I have a KT61 or an EL33
Mike

 
Posted : 05/09/2013 4:33 pm
Anonymous
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Also
http://frank.pocnet.net/

 
Posted : 05/09/2013 7:58 pm
Anonymous
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I think some of Duncans Amps schematics have been hijacked. If you go to schematics - Marshall and click on most of the amps schematics then you get some Spanish looking site. Does anybody know Duncan to tell him.
Mike

 
Posted : 05/09/2013 10:48 pm
Anonymous
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I think some of Duncans Amps schematics have been hijacked. If you go to schematics - Marshall and click on most of the amps schematics then you get some Spanish looking site. Does anybody know Duncan to tell him.
Mike

it is a 404 (URL not present) message in Italian but what is possibly expected there maybe can be found below - its not anything sinister other than these "free hosting" companies moving stuff around, and the Italian chap who was sharing the schematics has had all the links on his website changed due to this. OK not quite related to the radio output valve but it might be worth keeping track of the new link as it could be useful to somebody...

http://www.pierluigipollano.ilbello.com/Schematics.html

 
Posted : 05/09/2013 10:54 pm
Westcliff
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Thanks for all the links. I've seen most of them before, but not the one Michael sent, cheers Michael. :aad

As for the 6V6, it won't get thrown away; I collect them as spares for my Fender amps.

Thanks for the offer Mike. I think I'm okay for a KT61, but if I'm not, you will be the first to know.

After a quick look at the 1117, there's not much visibly wrong: some sticky push buttons and a broken dial drive. If I'm lucky, the wire part will be intact and I will only have to replace the cord. I hate fixing dial cords.

Gus.

 
Posted : 06/09/2013 12:37 am
Westcliff
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I removed the chassis tonight and discovered that the cathode resistor is wire-wound and 100 ohms. I wonder if the set was operated much with the 6V6/100 ohms combo and what would be the outcome if it was?

On the good news front, the tuning drive wire is intact, with one end connected to the drum. The cord part of the drive is missing. The underside of the chassis looks original and all of the wiring is in good condition.

The only potential bad news is that my KT61 has a loose base and rattles copiously, so my next job is to test all of the valves. I believe some of them may be hard to get.

Gus.

 
Posted : 16/09/2013 1:55 am
Anonymous
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The 6V6 would wear out quickly, the output transformer might burn out (or winding insulation damaged so it fails later), a valve or metal rectifier would be badly worn and the mains transformer could even burn out (or winding insulation damaged so it fails later).

it's the same effect as having a slightly (but not very) leaky grid audio coupling capacitor.

 
Posted : 16/09/2013 11:50 am
Westcliff
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The output valve will be replaced with a 25L6 which I found in my stash and which was very good when tested. The 100-ohm resistor has been replaced by a 180-ohm 2-watt resistor.

The tuning drive has been re-strung, a four-hour job the other night (and it's a fairly simple one too). :bbd

I have started cleaning the cabinet, which lived for some time in a smoky environment. My main aim is to preserve the perfect HMV transfer, so I have a question. Will all-purpose cleaning foam damage the transfer? I'm not going to touch the grille cloth because it is intact but grubby. I don't want it to be clean but torn.

As for replacing the waxies, that looks like it will be easy because of the sensible and spacious layout underneath the chassis.

Gus.

 
Posted : 03/10/2013 1:36 pm
Refugee
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Be careful with the transfer.
I have just cleaned the dial on a TR82 and I spotted a slight trace of the red dial colour on the cleaning cloth. It was enough for me to use caution. I was prepared to work fast if it needed to be dried fast. It did :cch

 
Posted : 03/10/2013 2:17 pm
Westcliff
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The transfer survived a squirt of foam and a fairly gentle wipe and the cabinet has had a wax polish. It looks much nicer now, some of the scratches have vanished.

Here are some "before" pictures.

Gus.

 
Posted : 04/10/2013 12:39 am
Cobaltblue
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The output valve will be replaced with a 25L6 which I found in my stash and which was very good when tested. The 100-ohm resistor has been replaced by a 180-ohm 2-watt resistor.
Gus.

Hi Gus did I miss something the 25L6 has a 26V filament.

Cheers

Mike T

I don't care if it was a bargain whats it doing on my kitchen table. www.cossor.co.uk

 
Posted : 04/10/2013 8:47 am
Refugee
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It depends on the letter(s) after the type number what the heater voltage is.
We need to see the full part number.
http://en.wikipedia.org/wiki/25L6

 
Posted : 04/10/2013 9:09 am
Cobaltblue
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I agree with Jeffrey

In this series the first numbers indicate the approximate filament voltage and this is pretty consistent in American numbered Octal valves.

The 50L6 has a 48V 0.16 V filament and the 6L6 is 6.3V 0.9A

Cheers

Mike T

I don't care if it was a bargain whats it doing on my kitchen table. www.cossor.co.uk

 
Posted : 04/10/2013 9:46 am
Refugee
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The 25L6 if clearly for an AC/DC set and another heater transformer would be needed for it to be used in an AC set.

 
Posted : 04/10/2013 10:02 am
Westcliff
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Sorry, I meant 6P25.

Gus.

 
Posted : 04/10/2013 12:11 pm
Refugee
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That makes a lot more sense :thumb

 
Posted : 04/10/2013 12:27 pm
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