| Posted by Art Grannell | October 08, 2018 - 05:35 pm |
| Brian, Thanks for your inquiry! Assuming that the new cathode resistors are very closely matched, the most probable cause for the difference between the two channels is the output tubes are not well matched. It may be worthwhile, if you feel comfortable doing this, to check the B+ voltage at pin 7 (to ground) of each output tube, with the input jacks shorted. The voltage may be a little higher or lower than Dyna's specified value of 370VDC, depending on your AC line voltage. All four tubes however, should measure within a few volts of the average reading. This should eliminate the possibility of a wiring problem in the B+ supply, or at the tube socket. One thing you can do, before ordering new tubes, is to try to get a better match by switching the positions of the individual output tubes, i.e., tube number 2 and 3 may more closely match numbers 1 and 4, etc. It seems that some tube sellers do a far better job of matching tubes correctly than others. Both Dave and I have found Jim McShane's tubes to be very well matched. |
| Posted by Brian | October 07, 2018 - 07:26 pm |
| Hi - I see this comment section hasn't had much activity for a while, but here goes anyway: I recently installed the EFB modification in a ST-35 that my dad built in 1963. The 6BQ5s are Realistic so they were changed at some point, but they still seem to be working OK. My question is in setting the bias correctly. As I understand the procedure, the average voltage measured should be 0.27 VDC. I was able to achieve that average, however to get that average I ended up measuring 0.175 on the LC and 0.362 on the RC. Although it averages to the required 0.27, there's quite a difference on each channel. Is this acceptable, or should I be looking at replacement tubes? Any thoughts or feedback would be appreciated! |
| Posted by Steve L. | June 12, 2013 - 01:59 pm |
| Hi James, I have replied on Facebook with Dave's email address. Very nice FB page, by the way. |
| Posted by James Fisher | June 12, 2013 - 09:37 am |
| Is there anyway I can get ahold of Dave Gillespie. I would love to show him how I'm using his design. And I ensure every purchaser is well a where of his design influence. I even did a write up for Georgia Tech on it. https://www.facebook.com/FisherAmps |
| Posted by Dave | March 08, 2012 - 09:18 am |
| Hi Lydia -- It is actual circuit design that has the lions share of influence on the sound a particular unit will have. The best designs will emloy design techniques and specifications that will inherently minimize the influence that any external devices can contribute to the performance achieved. The design of the SCA-35 encompasses these techniques. Therefore, such external items as cabling, dampeners, and the like become items of personal preference, as few of these items have any true scientific double blind testing behind them to allow support of any absolute recommendations. That is not to disparage them in any way, but simply to say that it is safest to assume that items marketed by subjective claims become items of personal preference by definition. Therefore, only you can be your own guide with such ancillary items. As for the tone control and input modifications for the SCA-35, check out the diytube site under the ST-35 section. There you will find various threads to address your questions regarding these issues. Answers to the rest of your questions can be found in the Dynaco owner's manual for the SCA-35, which is readily available on the web if you do not have one. Good luck with your restoration! Dave |
| Posted by Lydia | March 08, 2012 - 04:14 am |
| Hi Dave, Art, I am in the process of purchasing a restored SCA-35, and I was wondering if there is a lot of difference in N.O.S. tubes, and new ones? If new, which ones do you recommend? The 7199's I will have RCA's NOS. Only 6bq5/el84's I have to figure out the ones I am to go with.... It is a stock unit but he said that he added 5k trimmers to each output tube so that each one can be biased individually. I have built a pair of Jon Risch's Cross-connected speaker cables and I have already compared them to the Kimber 4pr, and the Risch's CC89269, is so transparent clearer, detailed mids and highs are more naturally present, especially jazz drum solos. It does lack in thiness in the bass, but maybe breaking it in will improve!? How do you think this will sound with my Advent 6003's they are really "Maestros" from 1982. probably the last year for the big heavy 3-way speakers with the gray donut ring midrange. any advice on where to proceed once I get the unit? Audioregenesis sells a neat board that fits in place of the can caps and comes with the EFB. is this a good idea or since I have almost finished my EFB,, board I really want to use mine. What about vibration? I am going to use Rubber Stoppers glued to the bottom giving a little firm cushion raised up about an inch on my wood cabinet, is this going to be good enough? any other recommendations are welcomed. Oh by the way, some people have bypassed the tone controls and sounded better do I have to do this since I am going to do the EFB.? also I want to know if I can run my CD/dvd Player and what input am I going to use? Can I make another input, or change the "head in" to plug another input device say Tv audio? can you run parralel speaker wires 2-pair going to left and right speakers? what about connecting 2-pairs of speakers running in series each side? |