UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Closed Thread
 
Thread Tools
Old 13th Dec 2018, 8:50 pm   #21
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
Default Re: Restoring/repairing a triode output valve

To reliably re-fire any remaining getter in the original getter-holder you will indeed need some form of induction-heater.

That assumes there's any getter-material left to re-fire. And that whatever fault has caused the original gettering to have failed is not still there....

TBH I'd be looking more at reworking the amplifier to use non-defective valves. I'm sure a couple of 6L6, KT66, 5B/254M could be engineered in there, either as grid-strapped pseudotriodes or with screens wired to HT as Mr. Sarnoff and friends always intended. Done properly I'd guess it would end up a lot louder than the triodes.
G6Tanuki is offline  
Old 13th Dec 2018, 8:52 pm   #22
GrimJosef
Dekatron
 
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
Default Re: Restoring/repairing a triode output valve

Pulsed laser deposition https://en.wikipedia.org/wiki/Pulsed_laser_deposition ?

Small-ish pulsed lasers are fairly readily available and allow you to 'place' energy very precisely without heating the surroundings much at all. There may well be a laser processing job-shop somewhere that would be prepared to have a go. Make sure you're absolutely clear about the hazards though. They blind in an instant.

Cheers,

GJ
__________________
http://www.ampregen.com
GrimJosef is offline  
Old 14th Dec 2018, 3:03 am   #23
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: Restoring/repairing a triode output valve

I'm not yet convinced that the valve is actually gassy. Without actually seeing it in action it's hard to tell. If it's just the slight blue tinge seen on the inside of the glass in a darkened room as I mentioned before, then I don't think there's too much to worry about and the problem is more likely to do with the actual heater connection in the base of the valve. On the other hand, if the whole inside of the valve seems to be glowing very blue, and can be seen under normal light, then that is bad news. The last power output valve that I saw doing that was an EL519 which would sometimes flash over as soon as HT was applied and blow the fuse in the unit it was in. Once it had stabilise and had stopped flashing over, it worked to an extent, but the blue glow was all around the internal electrode structure and seemed to light up the entire inside of the valve - now that WAS a gassy valve!
Techman is offline  
Old 14th Dec 2018, 2:41 pm   #24
Michael Maurice
Moderator
 
Michael Maurice's Avatar
 
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,219
Default Re: Restoring/repairing a triode output valve

The grid voltage is not at 0V and can vary up to 50V! Thats surely not good news.
__________________
Forum Moderator

http://www.michaelmauricerepairs.co.uk/
Michael Maurice is offline  
Old 14th Dec 2018, 3:06 pm   #25
GrimJosef
Dekatron
 
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
Default Re: Restoring/repairing a triode output valve

If that's +50V and the grid leak is not open-circuit then that indicates enormous grid current corresponding to very serious levels of gas in the valve. Normally I start to suck my teeth about grid current if it approaches a microamp and if I remember rightly the maximum of the Gas range on my AVO CT-160 is 5 microamps (if you know the grid leak resistance you can work out what positive grid voltage that corresponds to).

Cheers,

GJ
__________________
http://www.ampregen.com
GrimJosef is offline  
Old 14th Dec 2018, 3:15 pm   #26
Techman
Dekatron
 
Techman's Avatar
 
Join Date: Nov 2009
Location: Lincolnshire, UK.
Posts: 4,985
Default Re: Restoring/repairing a triode output valve

That doesn't sound good at all.

The thing I can't understand about this is what are 'CV' type numbered valves doing in this amplifier?

I suspect that sometime, perhaps recently, with all the talk of the value of the original valves, that someone has removed the original valves and sold them in exchange for a couple of 'supposed working well enough for a radiogram' type valves that are not worth very much, but unfortunately, one of them is a duffer - this could have happened before you were asked to look at the radiogram. I think some inquiries need to be made regarding its recent history, that's if it's the same gram as I think it is. Did the dust level on those valves match the level of dust on the rest of the innards of the gram and its chassis?
Techman is offline  
Old 14th Dec 2018, 11:05 pm   #27
Michael Maurice
Moderator
 
Michael Maurice's Avatar
 
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,219
Default Re: Restoring/repairing a triode output valve

Techman brings up a very valid and interesting point. The original output valves as marked on the chassis are PP3/250 so it has been 'got at' but with no other sign of tampering. The driver valves are original as is the rectifier valve as is all the valves on the radio chassis.

Given that this probably dates from the late 40's to very early 1950's it would probably have been fitted with a 78 only deck, something like a Garrard RC60 or RC70. What I found in there was a BSR UA6!

These valves may well have been changed a long time a go. To make matters slightly more difficult, I'm repairing this for a 3rd party who will not be the end user.
__________________
Forum Moderator

http://www.michaelmauricerepairs.co.uk/
Michael Maurice is offline  
Old 14th Dec 2018, 11:46 pm   #28
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: Restoring/repairing a triode output valve

So that brings up the question of what the owner wants. If he's of the "It must be triodes" view, then he's into big bucks territory. The audiophools have created high priced demand for all power triodes, so any exact, near or far equivalents are going to be pricy.

If his view is "I just want it working" then that opens the door to triode-strapped beam tetrodes.

I'm concerned about how reliable it would be if that existing valve was somehow brought back from the dead. I wouldn't want it to impact your reputation, Michael.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now  
Old 15th Dec 2018, 10:45 pm   #29
Michael Maurice
Moderator
 
Michael Maurice's Avatar
 
Join Date: Feb 2006
Location: Wembley, Middlesex
Posts: 7,219
Default Re: Restoring/repairing a triode output valve

The thing is, its not quite so easy to modify for triode strapped beam tetrodes is that it requires quite a few modifications.

PX4 et all have a 4V heater, beam tetrodes and pentodes use 6.3V heater.

The existing heaters have to be modified so that they are disconnected from the triodes.

A new transformer would have to be fitted, the valve bases would have to be changed, the cathode circuits would have to be somewhat reworked.

After carrying out all this work, it might be cheaper and easier to find a replacement valve.
__________________
Forum Moderator

http://www.michaelmauricerepairs.co.uk/
Michael Maurice is offline  
Old 15th Dec 2018, 10:57 pm   #30
GrimJosef
Dekatron
 
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,310
Default Re: Restoring/repairing a triode output valve

There are quite a few 4V tetrodes and pentodes. Some are directly heated and if you could find one with a loose base you could fit a B4 base and triode-strap inside it. Unfortunately most of the relatively high audio power ones take 2A from the heater supply rather than 1A and might overload the 'gram's mains transformer. I don't know if PP4s ever show up (apparently equivalent to Mullard PM24M http://www.r-type.org/exhib/aad0272.htm) or whether they might work anything like a PX4 if triode-strapped.

Cheers,

GJ
__________________
http://www.ampregen.com

Last edited by GrimJosef; 15th Dec 2018 at 11:23 pm.
GrimJosef is offline  
Old 18th Dec 2018, 7:18 am   #31
FrankB
Heptode
 
Join Date: Oct 2005
Location: Olympia, Washington, USA.
Posts: 663
Default Re: Restoring/repairing a triode output valve

Not being familiar with the diameter of your tube, but you might try to find a neon sign shop nearby, and ask them to use their induction heater on it to re-heat the tube and re-flash it.
Typically, all the gettering material does not get used up in the factory flashing process.
FrankB is offline  
Old 18th Dec 2018, 1:52 pm   #32
AC/HL
Dekatron
 
AC/HL's Avatar
 
Join Date: Nov 2003
Location: Heckmondwike, West Yorkshire, UK.
Posts: 9,637
Default Re: Restoring/repairing a triode output valve

If you search eBay for induction heater, there are several of varying powers. You'd need to experiment with the coil, which means it's probably not a quick fix, and the cheapies may not be powerful enough...
AC/HL is online now  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 5:23 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.