6550 Valve Differences - UK Vintage Radio Repair and Restoration Discussion Forum

DMcMahon · 24th Jan 2024, 11:12 am

Trying to find out the differences between a 6550, a 6550A and a 6550B, particularly their interchangeability. This is for use on an old Leslie Amplifier used with a Hammond organ.

Tried Googling but not very clear to me

David

Diabolical Artificer · 24th Jan 2024, 3:55 pm

AFAIK an "A" designation on American valves refers to a heater warm up characteristic or some other minor parameter difference or iteration. I'm thinking in terms of the 12BH7 & 12BH7A for instance. Having said that Mullard also used an A suffix, EG EF37 & EF37A. Also suffix's often referred to the envelope shape, EG G, GT etc.

With a modern valve it's probably there for bling, though I could be wrong, therefore if you can't find a major difference there probably isn't one.

Andy.

chriswood1900 · 24th Jan 2024, 5:38 pm

David
According to the US Tube Lore book (by Ludwell Sibley) the A designation was used to denote the T16 parallel sided envelope and 1.8A heater B and C were used by Svetlana and other later manufacturers of tubes. As long as you have a pair I don't think it would make any difference which designation you had.
In the GE 6550A data sheet the anode voltage is increased to 660 from 600 and screen from 400 to 440.
https://www.drtube.com/datasheets/6550a-ge1972.pdf

Joe_Lorenz · 24th Jan 2024, 9:18 pm

Hello,

have you already visited this site:

https://frank.pocnet.net/sheets61.html

I have been using 6550A (General Electric) in a pair of Jensen amplifiers and I can't complain about anything. Surely they will do their job in a Hammond organ Leslie, too. I daresay Mr Jon Douglas Lord would agree!

Joe

DMcMahon · 25th Jan 2024, 12:06 am

Thank you Chris and Joe, no had not previously seen the websites PDFs, very useful.

David

DMcMahon · 25th Jan 2024, 12:07 am

Quote:

Originally Posted by Joe_Lorenz

I daresay Mr Jon Douglas Lord would agree!

Joe

Yes but only sadly from the grave.

David

DMcMahon · 26th Jan 2024, 11:13 am

Evidently one of the original 6550A had partially fogged so assume had gone to air. The glass envelope broke when the valve was removed.

I am trying to get access to the Leslie amp to checkout the associated components and valve voltages.

David

Joe_Lorenz · 29th Jan 2024, 8:56 pm

It is always a good idea to check the surroundings of any component that has given in. Anyway, if a valve has got gassy there is not necessarily a bad component at fault, but well, it is better to check before replacing the valve.

I'm afraid NOS 6550A has become pretty expensive nowadays but the sound of your organ will justify the expense!

Joe

DMcMahon · 13th Feb 2024, 11:35 am

My friend replaced both 6550A with new 6550A despite me saying let me test the voltages/components first just in case. The Hammond/Leslie evidently is working fine now.

I am visiting him tomorrow, will take my meter and Leslie schematic in case there is an opportunity to do some testing, from previous work on his Leslie I seem to remember that not easy (access wise) to do live testing of the Leslie amplifier.

David

DMcMahon · 18th Mar 2024, 12:01 am

All valve voltages in the Leslie 145 amp today checked out all good. Leslie and Hammond tested OK afterwards.

David

toprepairman · 28th Mar 2024, 2:48 pm

Ooh I have one of those stashed away somewhere.

24th Jan 2024, 11:12 am	#1
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,607	6550 Valve Differences Trying to find out the differences between a 6550, a 6550A and a 6550B, particularly their interchangeability. This is for use on an old Leslie Amplifier used with a Hammond organ. Tried Googling but not very clear to me David

24th Jan 2024, 3:55 pm	#2
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,676	Re: 6550 Valve Differences AFAIK an "A" designation on American valves refers to a heater warm up characteristic or some other minor parameter difference or iteration. I'm thinking in terms of the 12BH7 & 12BH7A for instance. Having said that Mullard also used an A suffix, EG EF37 & EF37A. Also suffix's often referred to the envelope shape, EG G, GT etc. With a modern valve it's probably there for bling, though I could be wrong, therefore if you can't find a major difference there probably isn't one. Andy. __________________ Curiosity hasn't killed this cat...so far.

24th Jan 2024, 5:38 pm	#3
chriswood1900 Octode Join Date: Jan 2007 Location: Dorridge, West Midlands, UK. Posts: 1,486	Re: 6550 Valve Differences David According to the US Tube Lore book (by Ludwell Sibley) the A designation was used to denote the T16 parallel sided envelope and 1.8A heater B and C were used by Svetlana and other later manufacturers of tubes. As long as you have a pair I don't think it would make any difference which designation you had. In the GE 6550A data sheet the anode voltage is increased to 660 from 600 and screen from 400 to 440. https://www.drtube.com/datasheets/6550a-ge1972.pdf __________________ Chris Wood BVWS Member

24th Jan 2024, 9:18 pm	#4
Joe_Lorenz Hexode Join Date: Dec 2019 Location: Hohenroda, Eastern Hesse, Germany Posts: 462	Re: 6550 Valve Differences Hello, have you already visited this site: https://frank.pocnet.net/sheets61.html I have been using 6550A (General Electric) in a pair of Jensen amplifiers and I can't complain about anything. Surely they will do their job in a Hammond organ Leslie, too. I daresay Mr Jon Douglas Lord would agree! Joe

25th Jan 2024, 12:06 am	#5
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,607	Re: 6550 Valve Differences Thank you Chris and Joe, no had not previously seen the websites PDFs, very useful. David

26th Jan 2024, 11:13 am	#7
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,607	Re: 6550 Valve Differences Evidently one of the original 6550A had partially fogged so assume had gone to air. The glass envelope broke when the valve was removed. I am trying to get access to the Leslie amp to checkout the associated components and valve voltages. David Attached Thumbnails

29th Jan 2024, 8:56 pm	#8
Joe_Lorenz Hexode Join Date: Dec 2019 Location: Hohenroda, Eastern Hesse, Germany Posts: 462	Re: 6550 Valve Differences It is always a good idea to check the surroundings of any component that has given in. Anyway, if a valve has got gassy there is not necessarily a bad component at fault, but well, it is better to check before replacing the valve. I'm afraid NOS 6550A has become pretty expensive nowadays but the sound of your organ will justify the expense! Joe

13th Feb 2024, 11:35 am	#9
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,607	Re: 6550 Valve Differences My friend replaced both 6550A with new 6550A despite me saying let me test the voltages/components first just in case. The Hammond/Leslie evidently is working fine now. I am visiting him tomorrow, will take my meter and Leslie schematic in case there is an opportunity to do some testing, from previous work on his Leslie I seem to remember that not easy (access wise) to do live testing of the Leslie amplifier. David

18th Mar 2024, 12:01 am	#10
DMcMahon Dekatron Join Date: Apr 2019 Location: Worthing, West Sussex, UK. Posts: 6,607	Re: 6550 Valve Differences All valve voltages in the Leslie 145 amp today checked out all good. Leslie and Hammond tested OK afterwards. David Attached Thumbnails

28th Mar 2024, 2:48 pm	#11
toprepairman Tetrode Join Date: Jun 2021 Location: Leatherhead, Surrey, UK. Posts: 73	Re: 6550 Valve Differences Ooh I have one of those stashed away somewhere.