1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Valve Amplifier valve identification

Discussion in 'Tube Audio' started by fink lever, Dec 26, 2017.

  1. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,575
    Location:
    Southern NJ
    Random thought, but I do own a post-war EH Scott that uses a gas regulator tube to provide stable voltage to the FM tuner section to keep it from drifting. Not impossible thats what yours is doing.

    I think you're either going to need to find the schematics, or draw some up to figure out what you've got here. It looks well made, but all the transformers on it speak to being far more engineered than you'd get with typical consumer gear.
     
    Pio1980 likes this.

     

    Please register to disable this ad.

  2. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    Thanks for that Gadget73, i was thinking exactly the same...I would need to find an 'old guru' (as stated previously)
    - would love to here from anybody that could draw up a schematic as its far beyond me! I would be able to compensate their time and effort though....
     
  3. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    Hi, just wondering what gas regulator the E,H Scott amplifier is using and do you know the year or model amp? Wouldn't mind looking at it's setup...it sounds like an interesting amplifier
     
  4. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,096
    Location:
    Angel Station, Alabama
    Probably that of the 1947 E. H. Scott model 800b AM/ FM receiver, I'd assume a type 0D3 cold cathode gas regulator.
     
    Last edited: Dec 29, 2017
  5. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,575
    Location:
    Southern NJ
    Yes, OD3.

    nostalgiaair has the service literature for it. Its quite a lot of it too, most old radios you get a page or two, this one is 59 pages. Then there is the official factory service manual in 4 parts, total of 87 pages. They were definitely not shy about detailed circuit descriptions and operational theory.
     
    fink lever likes this.
  6. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    That is a large manual definitely...your amplifier is interesting to me as there may be many similarities to mine so will definitely check out the schematic.

    Is the Scott amplifier some sort of classic? It is very early design. I am in the UK so we don't get to hear much about early American Amplifiers.
     

     

    Please register to disable this ad.

  7. Dandy

    Dandy Super Member

    Messages:
    4,494
    Location:
    North West, UK
    Hi fink lever. Welcome and thanks for bringing such a beautiful bit of kit for us to marvel at. I think we have established that it's not a stereo amplifier, so there seem to be two amplifiers on the chassis supplying the two different speakers? It would help if you could confirm that, by seeing if both are being supplied by one power transformer. Maybe driving the different speakers for different frequencies? You might be able to determine which are output transformers (by their connection to the speakers) and which are chokes (linked to big caps as part of the power supply). The second pic in post #20 looks to be the secondary of a good quality output transformer.

    As this is an old, bespoke, British build, I would suggest that you ask for a good tech in your area via the UK Vintage Radio Repair and Restoration forum. They would also have vintage radio specialists who can advise on the AM and FM stages. The site is here: https://www.vintage-radio.net/forum/index.php
     
    fink lever likes this.
  8. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,096
    Location:
    Angel Station, Alabama
    It is the amplifier section of this radio receiver.
    https://antiqueradio.org/scot03.htm
     
  9. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,096
    Location:
    Angel Station, Alabama
    Scott did bespoke radio receivers in the 1930s, not dissimilar to how Rolls-Royce did business, particularly with the Phantom series.
    An exceptionally complex and exclusive example;
    http://www.campx.ca/dubois.html
     
    drtool and fink lever like this.
  10. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    Hi Dandy, thank you very much for your advice. I am glad you like the amplifier.
    When time permits (this week) I will take it out again and have a proper good look at the underneath.

    I think you are correct in that the AM amplifier is powered by the main amplifier. The AM amplifier though may have also an power valve as two are missing 1 with a cap.So does this make it a type of pre?

    I will also post some more pics as the cabinet housed a Garrard rc80 which fed into the into a small unit underneath the FM dials. Which also fed the speakers. I really need to draw out for everyone as I think once figured out quite an efficient setup. My new years resolution...
     
    Dandy likes this.
  11. Dandy

    Dandy Super Member

    Messages:
    4,494
    Location:
    North West, UK
    Keep us posted on your progress, questions and discoveries. If drawing up a schematic is daunting, then even a black diagram of the main parts would help.
     
    Pio1980 and fink lever like this.

     

    Please register to disable this ad.

  12. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    Thank you all for your input regarding my valve amplifier....
    Thank you Dandy for pointing me to the vintage-radio forum as the amplifier has now being taken for service and restoration. I will keep the you all posted on what we find and how the job of replacing caps etc goes. Also a Block Diagram will be posted to inform everyone of the layout. Lets hope everything goes smooth and if any of you would like to input or gain extra knowledge please post to let me know. Again watch this space as pics and extra info is posted.... many thanks and happy new year all!!!!
     
    Pio1980 likes this.
  13. Dandy

    Dandy Super Member

    Messages:
    4,494
    Location:
    North West, UK
    That's great news fink lever. We look forward to hearing more about your amplifier in due course.
     
    fink lever likes this.
  14. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    Valve update: a quick update of the initial observations by the tech guy.
    " There are one or two valves in the wrong places which had me a bit confused !
    There are effectively 2 power units on the chassis, with 2 separate mains transformers. There should be 2 rectifiers also, but one had been replaced with an output valve.

    The larger power supply provides power to the 2 push pull amplifiers ( 6 valves ) . one for each speaker.
    The two stab. valves are, as I suspected, used in series to provide a stabilised supply greater than one alone can manage. This is used for the ‘screen grid’ supply for the 4 output valves. This is truly ‘good design’

    The smaller power supply is used just to power the radio chassis, which also contains pre-amps for each of the 2 power amplifiers. If you think of the average power amp as having at least 4 valves, this guy has decided to split off the first preamp section and locate it on the radio chassis. This explains some of the extra valves here. With so many valves to light. the heater consumption is quite large, which is probably why he decided to use two transformers.

    The relay below the chassis took a while to fathom. But it’s quite clever To avoid the radio chassis power supply coming on AFTER the amplifier one and making a ‘plop’ the relay will only close and activate the power to the amplifiers, when the radio chassis power supply is completely active ( i.e. all valves warmed up ) As the rectifier for this power supply was missing, there was no supply to activate the relay , hence the stabiliser valves not glowing !
    That said, I have not powered it up completely ( other than applying mains to the empty chassis to test the transformers ) as all but one of the electrolytic capacitors have failed completely and will need replacing to make it safe.
    All the transformers ( and 3 chokes ) seem to be OK.

    The radio chassis is more of a puzzle, in addition to the usual radio stages, it appears to have a large pre-amp section , the additional valves may have something to do with amplifying the pickup signal. It is an above average radio design, with extra stages where it counts, to pull in the maximum amount of signals, Again here, there are a few valves missing/in the wrong place. Hopefully the valve holder connections will yield information about what valves should be where.

    The 2 power amps use 2 different pairs of valves, 6F6G and 6V6G. but this may have happened over time. The bias voltage is adjustable, with a rotary control .to ensure an exact match between both valves of the same amplifier.
    These may have to go, as the variable control takes a lot of current and could fail causing an overload and valve failure."

    So we are finally getting a picture
     
    drtool and Pio1980 like this.
  15. Dandy

    Dandy Super Member

    Messages:
    4,494
    Location:
    North West, UK
    Wow, that's impressive, and complex. I'm glad you've got a knowledgeable tech on the job, especially for sorting out the correct valves.

    Interesting that he confirms that one power supply is for the two separate power amplifiers which drive the two different speakers. I wonder if the two amps are the same and could be reconfigured for two matching speakers for stereo use?

    Interesting too that there is use a second, separate, power supply for the radio. It should sound amazing when all restored and running as intended.
     
    fink lever likes this.
  16. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    Very Happy at the moment....nice to figure out this setup as it was beyond me... The Tech guy is great and seems to be very knowledgeable so he should keep updating me...

    Regarding the amp I am not wanting to adapt it to Stereo although I think you can like you say. I am a mono fan and have been for a while. Most vinyl is played up to 1960s. If you played modern stuff I would have a little setup for that.

    Seriously though I think it's like a biwire or parallel mono but custom designed for am and FM which I would like to listen to more as I can't stand Dab radio.

    Also i was told by the tech guy that the design looks like it it was designed with the speakers in Mind first so I love goodmans and am looking forward to more updates.

    I do though have one issues in that my Neat turntable is a tight squeeze so may have to change it....
     
    Dandy likes this.

     

    Please register to disable this ad.

  17. jaymanaa

    jaymanaa AK Subscriber Subscriber

    Messages:
    54,348
    Location:
    OZ
    and the plot thickens. I would guess, that the 6V6 socket was originally intended for a 6F6 as it was very common to just "update" to a 6V6 when 6F6s failed. I would recommend going back to the 6F6s, and for what it's worth, Fivre had very nice ones if you can find a couple. I would also guess, that the output valve that used a top cap would be an 807, or on the way outside a 1625, filament voltage would tell you. I bet you could draw yourself a schematic, it just takes some time, but it's a really good way to familiarize yourself with the circuit. I do it in sections, like power supply, preamp, tuner, and output all on separate drawings. If those bad electrolytics failed to a short circuit, I'd check the rectifier and regulator tubes very closely, they could have taken a pretty big hit, did the fuses blow? I'm glad to see you are making such good headway, as these are very interesting.
     
    fink lever likes this.
  18. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,096
    Location:
    Angel Station, Alabama
    Top cap tube could be 6F8.
     
  19. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    Yes we are moving in the right direction...

    I will forward your message to my tech guy and see what he says...thanks a lot
     
  20. fink lever

    fink lever Member

    Messages:
    70
    Location:
    Surrey
    HA002.jpg Well done to the Tech Andy on the schematics!!!
     

    Attached Files:

Share This Page