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Ball Ground, GA
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Fisher SA-100 Clone, from Ball Ground, GA


Absolutely! Thanks for spotting that -- it's been corrected. Dave Apr 27, 2017

dcgillespie was last seen:
Jun 18, 2018 at 3:00 PM
    1. Fitzgreen505
      Hi Dave: I'd like to put an EFB into my Fisher 400, but I'm still not sure what components go into the EFB circuit. Perhaps I've missed something. Is there a schematic somewhere? Are you selling one?
      Thanks. Fitzgreen505
    2. njmpmcc
      Dave - I contacted you about 18 months ago about you updating/reconditioning my original Fisher 400, Serial #72,094, but you were busy. Would you please put me on it for working on my 400. It as been "resting" since about 1975, with the exception of a short ~1 minute run to check out its potential.. No problems then. As I am close to you in Roswell, I can bring the unit up to you any time.
    3. leland331
      Hey Dave, I'm doing some research and trying to put plans together to build an amp using transformers from an eico st-40. I am going to stay with the 7591 output tubes and will drive them with an ecc83 and a 6sn7. I would like to do something a little bit better than a simple cathode resistor and regulated screens.Then I came across EFB. Is there a way to implement it without getting too complicated? Thanks
      1. View previous comments...
      2. dcgillespie
        The change in current draw from 0 to full power doesn't change as much with cathode vrs fixed bias, but it does still change.

        Use cathode bias, but use the EFB screen grid regulator to power the screens. That will keep the screen grids locked into place relative to the plate supply regardless of the current they draw.

        You'll find examples of the EFB screen grid regulator in my Fisher 400 and X-101C threads.

        Nov 2, 2015
      3. leland331
        I reviewed your schematics and it seems to make overall sense to me. Couple quick questions though.
        I'll use your sa-100 as an example. the screen regulator portion, the source of FQP9n50c is attatched to the bias supply which i dont have. Do i omit that part of the connection?
        Nov 3, 2015
      4. dcgillespie
        Correct. Then you can tailor the resistor supplying the Gate to produce the screen voltage you want.

        Nov 3, 2015
    4. dcgillespie
      Hi Jim -- I am happy to help with your Pilot, but must tell you that at this point, I'm about 2 months out with firm commitments with existing clients -- after that, it's just inquiries, but of course the holiday season will be upon us by then so it's very hard at this point to establish a definite time I could do the work.

      Please understand that I am not trying to put you off in any way. But I wouldn't be fair to you if I told you to send it, and it just sat here for several months. I simply don't and won't work like that. I will be happy to put on on the waiting list, which costs nothing to do. This work is purely a hobby to fund my hobby, so if someone falls out of line for some reason, it doesn't affect me one way or the other. Everybody else just moves up. I'm sorry this may not be as quick as you would like, but this year has kept me jumping from right out of the chute. If you would like me to place you on the list, just let me know, and thanks for the interest!

    5. jgsulliv
      Hi Dave, I'm in contact with Redboy regarding an original condition Pilot 232 he has listed on Bartertown. I'd love to have it but it needs to be refreshed/ restored before it can be put into use. I asked him to recommend someone to restore the amp and he pointed me to you.
      Are you taking on restoration work and, if so, would you be able to tell me a price range for a top quality restore? If you are taking new work, I'll ask Nate to send the amp directly to you, if that works for you.
      Keeping my fingers crossed,
      Jim Sullivan
      (201) 303-4141
    6. Gregg7230
      Hello, I'm a new member and I just brought a sa-100 yesterday off eBay. I want to use this unit mainly to listen from my headphones. I'm in NY and apartments dictate discreet listening. Also I wAs unaware that I needed a pre-amp( just so anxious to score one). Superampman suggested a Emotiva control freak. I was thinking of a little bear p5. Any thoughts or suggestions you may have would be greatly appreciated. Again my main usage would be listening to headphones from my I-devices/digital sources. I want to thank you in advance for all the work you've done on them and if your selling kits or anything else please inform me of how they can be obtained. Thanks again and good night.
    7. adedeluca
      You can reach me at adedeluca@aol.com
      I really love this 200 B
    8. adedeluca
      You really know your fisher tuners
      I just got my father in laws 200B playing
      It is incredible
      I have only one Mullard 12At7 working in the output stage ,the other one just stop working
      Can 12Ax7 s be used there? Which brand do you remeconmend

    9. dcgillespie
      Hi Carl - Thanks for the kind words! Probably the most material I've written about the ST-70 is a thread entitled "Dynaco ST-70: Baseline Testing". It covers the complete design of the ST-70 from A to Z, pointing out its strengths, and weaknesses. If I only did one modification to the ST-70, it would be to convert the power supply to SS operation as addressed in that thread. Both the performance and durability of the amplifier will be greatly improved. There are an incredible number of modifications that can be done to the ST-70. Having a good understanding of the performance that the stock design represents will help you immensely in deciding what modifications might be best for you.

      Thanks for the interest!

    10. Eulipian
      Aloha from the 5-O Dave. I read the thread on the Dynaco ST-70. Whew! As a total noob most of it was over my head, but I did get some of the signal about the weakness of the single tube rectifier and wonder what you ended up doing, if anything. I am a weak person and got excited, thinking I could follow along with whatever mods your science suggested. Of course there was one on ebay and I paid too much for it, but that's not your fault. I have a number of questions and wonder where you start with a project like this after verifying values? If you could point me to your most relevant post, I'll save you the time of a reply. This is a great resource and you are obviously maximally skilled and not interested in magic parts or subjective assessments. This is my first tube amp. Ironically, I own and assembled a Hafler DH200. I was not aware of his involvement with the Dynaco. Thank you for any response.

      Carl Varady
      Honolulu HI
    11. soundwaves
      Hi Dave,
      I picked up an Fisher 500-C some 25-plus years ago. I used it for a while but then put it on a shelf since I thought I shouldn't play it too much since it was old. I've recently decided to get it restored. It works, the tubes test well and are all original (the receiver is in good stock shape). I've been doing a lot of reading on these AK forums, and while I've found a tech guy near me (I live in Queens,NY), but after reading some stories here about repair jobs done inadequately or inexpertly I am wary. Your posts are plentiful and informative and show a love for these Fishers, and then I came across a poster speaking well of your restorations. So I'm writing to ask if you do restorations like this or if that was just a personal job. I'm not sure how msg's like this work in AK, but you can also reach me at pagerept@aol.com ... Thanks, Jim
    12. dcgillespie
      Hi Martin -- Thanks for the complement!

      Actually, I am completely self taught. I have read all the "bibles" of vacuum tube design from cover to cover so many times that their covers are now off. I have volumes of lab books from performing experiments to prove, or explain all that I learned. Therefore, I didn't concentrate so much on Fisher, as I did on theory and principle of operation. As a result, it really doesn't matter what brand I'm dealing with.

      The other aspect of my learning is that this is a hobby I have been intensely interested in all of my life. Its has spanned 55+ years, over which time I have accumulated and studied most of the published works of McIntosh, Hafler, Laurent, Crowhurst, Williamson, Keroes, Langford Smith, Tremaine, and so many others. In essence then, I formulated my own training program that was tailored specifically to my field of interest. It is a hobby I enjoy as much if not more than I did when I first saw a tube!

    13. vintelectra
      Hi Dave: How did you became so knowledgeable in electronics, particularly in Fisher? Martin
    14. david salty
      david salty
      Dave,. so in reading your MO200A build I have a question Sorry I'm one of those people who has to see it or ask a 100 questions as my brain just doesn't pick things up from reading or listening alone. on output ohm by changing the GRN 16 ohm to ground, Blk ground now 16 tap and 25vct green is now a 8 / 7.6 ohm. Now do I have to change other stuff too (keep in mind keeping setup stock)
    15. ronton3
      Hi Dave, Thanks for calling my attention to the fact that I can post to individual messages, I had been updating the original(live and Learn). I have new shots of the tone controls and others on the last post. Thanks for all your help. ron
    16. vanwinkle52
    17. vanwinkle52
      Bopgen MO100A phase inverter for 6550's


      I've modded a Bogen MO100a to use 6550's for outputs. I got the advice below from dcgillespe.

      6550s would also work just fine in this unit -- the high plate voltage is nothing they could not easily handle in stride, but the phase inverter stage would need a serious injection of steroids to develop the significant low impedance drive these tubes require. At a minimum, it would require powering it from a new (~ 500 volt) B+ point developed off of the output stage plate B+ source, and possibly splitting the 7247 into two separate tubes to really get the job done. A 6AV6 could be used for the input section without any changes, and 1/2 or even paralleled 12BH7 sections could handle the inverter service, with plenty of low distortion reserve drive capability for PPP pentode connected 6550 tubes.

      Name: Amp-Williamson-3.gifViews: 8Size: 18.8 KB
      ID: 427233
    18. Rod Beauvex
      Rod Beauvex
      What do you think would be the maximum wattage you could trick out of those Dynaco z565s?
    19. Rod Beauvex
      Rod Beauvex
      Thanks again for your concise answer. It's always a treat to hear you speak. Or type, as the case may be, whether it be article or or forum post.
    20. Rod Beauvex
      Rod Beauvex
      Just wanted to say thanks for all the concise answers to my questions. I'm sure you've got to be tired of seeing my name in the tube forum. :P
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    Ball Ground, GA
    Restaurant owner
    Kids are grown, I'm single, and enjoying life!

    VT audio and cars!