Heathkit IM5228 Valve Voltmeter - UK Vintage Radio Repair and Restoration Discussion Forum

TNC · 13th Jul 2006, 11:21 pm

Have just bought one of these - and after working for a few minutes it has promptly died!! However, having taken a look inside I have been intrigued to find there are no conventional valves in it, but in their place a pair of stainless-steel, 7 pin components that look a little like oversized AF115s - about 0.6" tall and 0.45" in diameter. they are marked TR1119 7725 and TR1002 7724...what on earth are they??

Grateful for any elucidation!

Trevor.

Duke_Nukem · 14th Jul 2006, 8:34 am

Do they look anything like these ? :-

Nuvistor

TTFN,
Jon

ppppenguin · 14th Jul 2006, 8:56 am

I'm sure Jon's right. They must be nuvistors.

Nuvistors were also used in 'scope front ends. They were the last generation of small signal valves that attempted to hold back the tide of silicon. Even at the end of the 1960s transistors could offer lower noise and better gain-bandwidth products than valves for virtually all small signal applications.

A VVM front end needs high input impedance which means valves or FETs. Good low noise wide bandwidth FETs came a bit later than bipolars. While a VVM does not usually need either of these qualities a nuvistor may well have been cheaper than a FET for a while.

TNC · 14th Jul 2006, 10:06 am

Thanks chaps! Now I see that's exactly what they are...any views on reliability/availability??

Thanks,
Trevor.

XTC · 14th Jul 2006, 11:07 am

They're very reliable and were used in a lot of high end kit in the 60s and early 70s, but they are valves and suffer from low emission after a lot of use.

You can buy them from the valve dealers. Some of them are pretty dear, £20 or more.

However, from what you've posted so far, it's by no means certain that the nuvistors are the problem. It would be as well to check the heater supplies are 6.3 - which is probably what they are supposed to be, then check through the circuit. It might be a dry joint or an O/C resistor.

Pete.

TNC · 14th Jul 2006, 12:35 pm

Thanks Pete - yes I am sure you are right so I am about to take a look at the machine but as I am still awaiting receipt of the manual it's a tad tricky

.
The pin-outs would be a help but I can't even find that info!
The nuvistors on the various websites look dimensionally about the same although the ones in this machine are 7 pin (the those elsewhere on the web seem mostly to be 5?) and also, there is no extensions to the casing that appear on the others. The ID numbers too are different and I haven't managed to trace them - I assume one is a double-diode and the other a triode.
atb
Trevor.

XTC · 14th Jul 2006, 3:01 pm

Quote:

Originally Posted by TNC

Thanks Pete - yes I am sure you are right so I am about to take a look at the machine but as I am still awaiting receipt of the manual it's a tad tricky

.
The pin-outs would be a help but I can't even find that info!
The nuvistors on the various websites look dimensionally about the same although the ones in this machine are 7 pin (the those elsewhere on the web seem mostly to be 5?) and also, there is no extensions to the casing that appear on the others. The ID numbers too are different and I haven't managed to trace them - I assume one is a double-diode and the other a triode.
atb
Trevor.

Are you sure that 7724 and 7725 don't refer to date codes? All the nuvistors I've seen have the type impressed into the top of the metal cap. The date code is often a year week date printed on the side. Most nuvistors were triodes, there was the odd tetrode, but I've never heard of a double triode nuvistor. 7586 and 6CW4 are widely used nuvistors.

They are covered in one of the 60s RCA valve data books. If you get really stuck, I can scan the page for you, however, I'd have thought that information would be already on the WWW somewhere.

Anyway, there's not much you can do with this VVM until you get hold of the manual.

Quote:

Originally Posted by TNC

The nuvistors on the various websites look dimensionally about the same although the ones in this machine are 7 pin (the those elsewhere on the web seem mostly to be 5?) and also, there is no extensions to the casing that appear on the others.
Trevor.

As far as I know, nuvistors all used a standard socket, and have two metal extensions, one wider that the other to make sure they go into the socket the right way and to make sure the delicate pins are guided into their sockets properly.

Are you sure these things are nuvistors?

Most of the nuvistors I've seen were made by RCA, although I think that Raytheon and a few other US firms also made them.

Pete.

ppppenguin · 14th Jul 2006, 3:08 pm

Data on 6CW4 and 7586 are both available in the excellent and free Duncan's Amps TDSL.

http://www.duncanamps.com/tdslpe/

This resource deserves to be clearly signposted both here and in other vintage wireless websites. It is an incredibly valuable collection of valve and CRT data with links to a huge number of scanned data sheets.

A list of some Nuvistor types can be found here:

http://en.wikipedia.org/wiki/Nuvistor

TNC · 14th Jul 2006, 3:45 pm

I am starting to query whether they are Nuvistors at all - the data is printed on the top of each - one is marked TR1119 and then below that the number 7725 and the other is marked TR1002 and then below that the number 7724.
I have found a reference to a 7724 in my Taylor 45D tester book - that states it's a double-diode...both devices fit in B9A sockets. What else could they be I wonder? To add to the confusion I now find that the 7724 is listed on page 12 of vol. 5 of the G.C.Arnold radio valve guide - under Triode Amplifiers!

Confused!

ppppenguin · 14th Jul 2006, 4:03 pm

7724 via TDSL:

http://www.pmillett.com/tubedata/HB-...7724_14GT8.PDF

Looks like a double triode but it's an ordinary size glass B9A.

XTC · 14th Jul 2006, 4:04 pm

Possibly matched transistors in the same can. They were used in that sort of kit in the 70s. They were often socketed. I suppose they could even be ICs. Some ot the early ones were put in cans rather than DIL packages.

Although, this is a VTVM.

You'll know for sure when you get the manual.

Pete.

TNC · 15th Jul 2006, 12:26 am

Well it's been an intriguing day! Having checked the voltages and the wiring around these "valves" - and having noticed that one "valve" was a 9 pin and one a 7 pin (sorry about earlier mis-information), to me, the v.t.meter looked very much like an earlier Heathkit model I own - the V-7A/UK .
That operates with a 6AL5 (EB91) {7pin} and a 12AU7 (ECC82). {9 pin}...I reasoned that maybe these strange stainless-steel "valves" are the equivalent of the 6AL5 and 12AU7...so I plugged in a couple I had by me!!
Not only did it not go "bang"...but the change also cleared the fault condition!
Which I think it rather proves S. Holmes's famous observation (which no doubt I will quote badly) - that when all the obvious has been eliminated...what remains, however unlikely, must be the solution!
Thanks for your patience and assistance.
atb
Trevor.

XTC · 15th Jul 2006, 10:46 am

Quote:

Originally Posted by TNC

Well it's been an intriguing day! Having checked the voltages and the wiring around these "valves" - and having noticed that one "valve" was a 9 pin and one a 7 pin (sorry about earlier mis-information), to me, the v.t.meter looked very much like an earlier Heathkit model I own - the V-7A/UK .
That operates with a 6AL5 (EB91) {7pin} and a 12AU7 (ECC82). {9 pin}...I reasoned that maybe these strange stainless-steel "valves" are the equivalent of the 6AL5 and 12AU7...so I plugged in a couple I had by me!!
Not only did it not go "bang"...but the change also cleared the fault condition!
Which I think it rather proves S. Holmes's famous observation (which no doubt I will quote badly) - that when all the obvious has been eliminated...what remains, however unlikely, must be the solution!
Thanks for your patience and assistance.
atb
Trevor.

Curiouser and curiouser. I asume these things are on B9A and B7G bases and that's how you were able to make the subsitutuion so easily. Nuvistor bases are very distinctive and much amaller. The sockets used for ICs and dual transistors were different again and nothing like a valve base.

There were a few solid state circuits made up in metal cases on valve bases as valve replacements. For the EB91, it's easy to see that they could have used a pair of diodes.

Anyway, finding that they are not nuvistors is a cause tor relief.

It would be interesting to see a picture of these items, if you have a digital camera.

Pete.

TNC · 15th Jul 2006, 12:08 pm

I have taken a couple of shots of these devices - it will be interesting to see if anyone else has come across them.

Trevor.

mickjjo · 15th Jul 2006, 1:11 pm

I believe these things were known as "Fetrons", solid state replacements for valves. There is a bit about them in "Practical Wireless", May 1973 issue.
A note about them mentioning Heathkit appears here:-

http://listserv.tempe.gov/admin/WA.E...th&F=P&P=26876

Regards, Mick.

mickjjo · 15th Jul 2006, 2:38 pm

Furthur delving into the Heathkit archives, the threads at number 224, (VTVM mod), reveals that the replacement of the 6AL5 and 12AU7 in valve voltmeters with "Fetrons" was a common Heathkit modification :-

http://listserv.tempe.gov/admin/WA.E...nd9802&L=heath

Regards, Mick.

.

XTC · 15th Jul 2006, 2:58 pm

Thanks, that's fascinating.

I've seen a commercially made semiconductor replacement for I think an ECL82, but it was nothing like as neat as those. It was a sizeable square box on a valve base.

Pete.

igranic · 15th Jul 2006, 10:09 pm

It seems that your IM-5228 may have been fitted with the IMA-18-1 'Fetron' modifcation kit available for many of the Heathkit VTVMs.

The objective was to provide instant warm-up and zero drift. IIRC, the modified VTVMs had a reputation for failing if used (with the appropriate HV probe) for measuring EHT.

After searching through my Heathkit documentation files I found the following typescript instructions for the upgrade kit.

CONTENTS:

TR1002SS Diode, part No. 150-57 (to replace 6AL5)
TR1119SS Triode, part No. 150-58 (to replace 12AU7)
10 Megohm resistor, part No. 1-40 (to replace 22 Megohm resistor in 6AL5 circuit)

INSTRUCTIONS:

( ) Unplug VTVM from the AC Outlet

( ) Refer to your Manual's "Final Assembly" steps and remove the back cover or remove the instrument from its cabinet

( ) Use the partial schematic below and locate the 22Mohm (red-red-blue) resistor at location "A". Remove this 22 Megohm resistor and replace it with the 10 Megohm (brown-black-blue) resistor supplied with this Modification kit.

( ) Your VTVM may or may not have a 22 Megohm (red-red-blue) resistor at location "B". If your VTVM does have this resistor, cut it out and discard it. Do not replace this resistor.

( ) Remove the 6AL5 and 12AU7 vacuum tubes from their sockets

( ) Install the TR1002 SS diode (#150-57) in the 6AL5, 7 pin tube socket

( ) Install the TR1119 SS diode (#150-58) in the 12AU7, 9 pin tube socket

END

With the help of the Fetron data sheets, it should be possible to fabricate substitutes using modern discrete components.

TNC · 16th Jul 2006, 12:01 am

Thanks to all for such interesting feedback - especially finding the details of the entire modification when fitting the Fetrons.
After re-fitting the valves, the ohms measurement is OK but after trying to recalibrate volts, I have noticed that AC volts read distinctly low - which I presume must be the result of the resistance changes which I will now alter back to original.

Thanks again,
Trevor.

XTC · 16th Jul 2006, 1:59 pm

Quote:

Originally Posted by TNC

Thanks to all for such interesting feedback - especially finding the details of the entire modification when fitting the Fetrons.
After re-fitting the valves, the ohms measurement is OK but after trying to recalibrate volts, I have noticed that AC volts read distinctly low - which I presume must be the result of the resistance changes which I will now alter back to original.

Thanks again,
Trevor.

Thanks for an interesting post altogether. I'd never heard of Fetrons, but had seen an example or two of these solid-state replacements for valves - which I assumed weren't that successful. However, given the times, it was a rational idea. Nuvistors and Heathkit don't quite go together for some reason - call it conservative engineering - but they don't.

If you're renovating a meter, it's worth investigating the resistors. Maplins do (or used to do) a range of 1% metal film 0.6 W resistors which were very stable and much better than the original fitted to most instruments. I've found that particularly the resistors, but just about all the passive components in old meters, show very strange behaviour when they start to get warm.

bye,

Pete.

14th Jul 2006, 8:34 am	#2
Duke_Nukem Octode Join Date: Jan 2003 Location: Birmingham, West Midlands, UK. Posts: 1,268	Re: Heathkit IM5228 Valve Voltmeter Do they look anything like these ? :- Nuvistor TTFN, Jon

14th Jul 2006, 8:56 am	#3
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Heathkit IM5228 Valve Voltmeter I'm sure Jon's right. They must be nuvistors. Nuvistors were also used in 'scope front ends. They were the last generation of small signal valves that attempted to hold back the tide of silicon. Even at the end of the 1960s transistors could offer lower noise and better gain-bandwidth products than valves for virtually all small signal applications. A VVM front end needs high input impedance which means valves or FETs. Good low noise wide bandwidth FETs came a bit later than bipolars. While a VVM does not usually need either of these qualities a nuvistor may well have been cheaper than a FET for a while.

14th Jul 2006, 10:06 am	#4
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Re: Heathkit IM5228 Valve Voltmeter Thanks chaps! Now I see that's exactly what they are...any views on reliability/availability?? Thanks, Trevor.

14th Jul 2006, 11:07 am	#5
XTC Retired Dormant Member Join Date: Oct 2004 Location: Bristol, UK. Posts: 837	Re: Heathkit IM5228 Valve Voltmeter They're very reliable and were used in a lot of high end kit in the 60s and early 70s, but they are valves and suffer from low emission after a lot of use. You can buy them from the valve dealers. Some of them are pretty dear, £20 or more. However, from what you've posted so far, it's by no means certain that the nuvistors are the problem. It would be as well to check the heater supplies are 6.3 - which is probably what they are supposed to be, then check through the circuit. It might be a dry joint or an O/C resistor. Pete.

14th Jul 2006, 12:35 pm	#6
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Re: Heathkit IM5228 Valve Voltmeter Thanks Pete - yes I am sure you are right so I am about to take a look at the machine but as I am still awaiting receipt of the manual it's a tad tricky . The pin-outs would be a help but I can't even find that info! The nuvistors on the various websites look dimensionally about the same although the ones in this machine are 7 pin (the those elsewhere on the web seem mostly to be 5?) and also, there is no extensions to the casing that appear on the others. The ID numbers too are different and I haven't managed to trace them - I assume one is a double-diode and the other a triode. atb Trevor.

13th Jul 2006, 11:21 pm	#1
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Heathkit IM5228 Valve Voltmeter Have just bought one of these - and after working for a few minutes it has promptly died!! However, having taken a look inside I have been intrigued to find there are no conventional valves in it, but in their place a pair of stainless-steel, 7 pin components that look a little like oversized AF115s - about 0.6" tall and 0.45" in diameter. they are marked TR1119 7725 and TR1002 7724...what on earth are they?? Grateful for any elucidation! Trevor.

14th Jul 2006, 3:08 pm	#8
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Heathkit IM5228 Valve Voltmeter Data on 6CW4 and 7586 are both available in the excellent and free Duncan's Amps TDSL. http://www.duncanamps.com/tdslpe/ This resource deserves to be clearly signposted both here and in other vintage wireless websites. It is an incredibly valuable collection of valve and CRT data with links to a huge number of scanned data sheets. A list of some Nuvistor types can be found here: http://en.wikipedia.org/wiki/Nuvistor

14th Jul 2006, 3:45 pm	#9
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Re: Heathkit IM5228 Valve Voltmeter I am starting to query whether they are Nuvistors at all - the data is printed on the top of each - one is marked TR1119 and then below that the number 7725 and the other is marked TR1002 and then below that the number 7724. I have found a reference to a 7724 in my Taylor 45D tester book - that states it's a double-diode...both devices fit in B9A sockets. What else could they be I wonder? To add to the confusion I now find that the 7724 is listed on page 12 of vol. 5 of the G.C.Arnold radio valve guide - under Triode Amplifiers! Confused!

14th Jul 2006, 4:03 pm	#10
ppppenguin Retired Dormant Member Join Date: Dec 2003 Location: North London, UK. Posts: 6,168	Re: Heathkit IM5228 Valve Voltmeter 7724 via TDSL: http://www.pmillett.com/tubedata/HB-...7724_14GT8.PDF Looks like a double triode but it's an ordinary size glass B9A.

14th Jul 2006, 4:04 pm	#11
XTC Retired Dormant Member Join Date: Oct 2004 Location: Bristol, UK. Posts: 837	Re: Heathkit IM5228 Valve Voltmeter Possibly matched transistors in the same can. They were used in that sort of kit in the 70s. They were often socketed. I suppose they could even be ICs. Some ot the early ones were put in cans rather than DIL packages. Although, this is a VTVM. You'll know for sure when you get the manual. Pete.

15th Jul 2006, 12:26 am	#12
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Re: Heathkit IM5228 Valve Voltmeter Well it's been an intriguing day! Having checked the voltages and the wiring around these "valves" - and having noticed that one "valve" was a 9 pin and one a 7 pin (sorry about earlier mis-information), to me, the v.t.meter looked very much like an earlier Heathkit model I own - the V-7A/UK . That operates with a 6AL5 (EB91) {7pin} and a 12AU7 (ECC82). {9 pin}...I reasoned that maybe these strange stainless-steel "valves" are the equivalent of the 6AL5 and 12AU7...so I plugged in a couple I had by me!! Not only did it not go "bang"...but the change also cleared the fault condition! Which I think it rather proves S. Holmes's famous observation (which no doubt I will quote badly) - that when all the obvious has been eliminated...what remains, however unlikely, must be the solution! Thanks for your patience and assistance. atb Trevor.

15th Jul 2006, 12:08 pm	#14
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Re: Heathkit IM5228 Valve Voltmeter I have taken a couple of shots of these devices - it will be interesting to see if anyone else has come across them. Trevor. Attached Thumbnails

15th Jul 2006, 1:11 pm	#15
mickjjo Rest in Peace Join Date: Jul 2004 Location: Dartford, Kent, UK. Posts: 1,661	Re: Heathkit IM5228 Valve Voltmeter I believe these things were known as "Fetrons", solid state replacements for valves. There is a bit about them in "Practical Wireless", May 1973 issue. A note about them mentioning Heathkit appears here:- http://listserv.tempe.gov/admin/WA.E...th&F=P&P=26876 Regards, Mick.

15th Jul 2006, 2:38 pm	#16
mickjjo Rest in Peace Join Date: Jul 2004 Location: Dartford, Kent, UK. Posts: 1,661	Re: Heathkit IM5228 Valve Voltmeter Furthur delving into the Heathkit archives, the threads at number 224, (VTVM mod), reveals that the replacement of the 6AL5 and 12AU7 in valve voltmeters with "Fetrons" was a common Heathkit modification :- http://listserv.tempe.gov/admin/WA.E...nd9802&L=heath Regards, Mick. .

15th Jul 2006, 2:58 pm	#17
XTC Retired Dormant Member Join Date: Oct 2004 Location: Bristol, UK. Posts: 837	Re: Heathkit IM5228 Valve Voltmeter Thanks, that's fascinating. I've seen a commercially made semiconductor replacement for I think an ECL82, but it was nothing like as neat as those. It was a sizeable square box on a valve base. Pete.

15th Jul 2006, 10:09 pm	#18
igranic Rest in Peace Join Date: Jan 2005 Location: North Bedfordshire, UK. Posts: 395	Re: Heathkit IM5228 Valve Voltmeter It seems that your IM-5228 may have been fitted with the IMA-18-1 'Fetron' modifcation kit available for many of the Heathkit VTVMs. The objective was to provide instant warm-up and zero drift. IIRC, the modified VTVMs had a reputation for failing if used (with the appropriate HV probe) for measuring EHT. After searching through my Heathkit documentation files I found the following typescript instructions for the upgrade kit. CONTENTS: TR1002SS Diode, part No. 150-57 (to replace 6AL5) TR1119SS Triode, part No. 150-58 (to replace 12AU7) 10 Megohm resistor, part No. 1-40 (to replace 22 Megohm resistor in 6AL5 circuit) INSTRUCTIONS: ( ) Unplug VTVM from the AC Outlet ( ) Refer to your Manual's "Final Assembly" steps and remove the back cover or remove the instrument from its cabinet ( ) Use the partial schematic below and locate the 22Mohm (red-red-blue) resistor at location "A". Remove this 22 Megohm resistor and replace it with the 10 Megohm (brown-black-blue) resistor supplied with this Modification kit. ( ) Your VTVM may or may not have a 22 Megohm (red-red-blue) resistor at location "B". If your VTVM does have this resistor, cut it out and discard it. Do not replace this resistor. ( ) Remove the 6AL5 and 12AU7 vacuum tubes from their sockets ( ) Install the TR1002 SS diode (#150-57) in the 6AL5, 7 pin tube socket ( ) Install the TR1119 SS diode (#150-58) in the 12AU7, 9 pin tube socket END With the help of the Fetron data sheets, it should be possible to fabricate substitutes using modern discrete components.

16th Jul 2006, 12:01 am	#19
TNC Hexode Join Date: Apr 2003 Location: Westcliff-on-Sea, Essex, UK. Posts: 386	Re: Heathkit IM5228 Valve Voltmeter Thanks to all for such interesting feedback - especially finding the details of the entire modification when fitting the Fetrons. After re-fitting the valves, the ohms measurement is OK but after trying to recalibrate volts, I have noticed that AC volts read distinctly low - which I presume must be the result of the resistance changes which I will now alter back to original. Thanks again, Trevor.