dcgillespie
Last Activity:
Aug 18, 2017 at 12:58 PM
Joined:
Mar 12, 2010
Messages:
8,678
Likes Received:
548
Trophy Points:
113
Location:
Ball Ground, GA
Occupation:
Restaurant owner

Share This Page

dcgillespie

Fisher SA-100 Clone, from Ball Ground, GA

Subscriber

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

dcgillespie was last seen:
Engaged in conversation, Aug 18, 2017 at 12:58 PM
    1. dcgillespie
      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!

      Dave
    2. Eulipian
      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
    3. soundwaves
      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
    4. dcgillespie
      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!

      Dave
    5. vintelectra
      vintelectra
      Hi Dave: How did you became so knowledgeable in electronics, particularly in Fisher? Martin
    6. 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)
    7. ronton3
      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
    8. vanwinkle52
      vanwinkle52
    9. vanwinkle52
      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
    10. Rod Beauvex
      Rod Beauvex
      What do you think would be the maximum wattage you could trick out of those Dynaco z565s?
    11. 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.
    12. 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
    13. dcgillespie
      dcgillespie
      Hi Mike -- If you are referring to the IN4007 diode, it is perfect for the job. Some will make much hay out of using the "fast recovery" version of this diode, but the claims made are theoretical only. To this day, I have never been able to capture, measure, hear, or otherwise substantiate the claim that the FR versions are superior. But as you know, there is a very fickle side of this hobby, so you can judge for yourself!

      Dave
    14. TubeJunkie
      TubeJunkie
      Hi Dave,
      On my 800-B / The two silver top-hat looking diodes, (refer to my "800-B restore question" Thread for photo) can those be replaced with 14007 diodes? Thank You. Mike
    15. TubeJunkie
      TubeJunkie
      Hey Dave,
      I hope your getting to finally rest a little after the move. I just finished the other 100AZ amp, they sound great. I really do appreciate your help. The world needs more guy's like you.

      I just picked up a nice Fisher 800-B reciever, off of Craigslist. Got it at a pretty good deal. Check out my latest thread, I posted a picture of it. I'd like your input on it. I have a couple questions about the 800-B. When you have time, of course. I found a video on YouTube of a guy with lots of test gear, working with a 800-B, just wondering if that was you? Talk to you soon. Mike
    16. TubeJunkie
      TubeJunkie
      Dave,
      Scratch that last message. I read the entire thread, and it made sense. So, I got everything wired up and I've been listening to the amp for over an hour now. It sounds great. I hope to start on the other 100AZ soon. Anyway, I've taken up enough of your time. As I said before, "Thanks is not enough, Dave" I really appreciate your help and guidance. If I can ever return the favor, just say the word. Talk to you soon my friend,
      Mike / TubeJunkie
  • Loading...
  • Loading...
  • About

    Location:
    Ball Ground, GA
    Occupation:
    Restaurant owner
    Kids are grown, I'm single, and enjoying life!

    VT audio and cars!