JL Sargent Posted June 24, 2011 Author Share Posted June 24, 2011 What I'm doing is using a Fluke 87V multimeter which has a high resolution mode (20,000 count) to match the suggested resistors to 2% or better yet 1%. I found this interesting article about it. http://www.tangentsoft.net/audio/resmatch.html Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 24, 2011 Share Posted June 24, 2011 The areas of the circuit where matching was advised is where the phase inverter splits the positive and negative half of the wave form before the music signal (wave form) is handed to the push pull pair of output tubes... half the signal is handed to each output tube for brute force amplification which is then rejoined in the output transformer. If this signal is not as equal as possible in all respects the defect will be compounded by the amplication factor of the output section. This equals big distortion numbers and generally bad sound. This is where push pull amplifier get most of there bad rep from the single ended guys... I've found that just about every single ended lover (not all) when asked what push pull amplifier they have auditioned you always get back either a few budget modern PP amps or vintage PP amps that are usually in need of a blue print type rebuild (and usualy also built to a budget). Matching key resistors and capacitors in a circuit is similar to blueprinting a high peformance motor build up. In amplifiers I design I even go a step further and install trim pots to allow me to match the circuit to the actaul tube used. I'm an ex drag racer from way back! My forum handle when I first stuck my nose into this loony bin was NOS440... Nitrous Oxide System and 440 cubic inches. Hence the reason my company name ended up NOS Valves but that Idea was born from the web page designer that first put together my website. Quote Link to comment Share on other sites More sharing options...
artarama Posted June 24, 2011 Share Posted June 24, 2011 In amplifiers I design I even go a step further and install trim pots to allow me to match the circuit to the actaul tube used. Nice! FYI, I always thought NOS stood for New Old Stock, cool back story. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 25, 2011 Share Posted June 25, 2011 In amplifiers I design I even go a step further and install trim pots to allow me to match the circuit to the actaul tube used. Nice! FYI, I always thought NOS stood for New Old Stock, cool back story. Well it does now! Quote Link to comment Share on other sites More sharing options...
davis419b Posted June 25, 2011 Share Posted June 25, 2011 ( Quote ) I'm an ex drag racer from way back! My forum handle when I first stuck my nose into this loony bin was NOS440... Nitrous Oxide System and 440 cubic inches. Hence the reason my company name ended up NOS Valves but that Idea was born from the web page designer that first put together my website. For some reason I dont think the 440 was Mopar, I think it was Chevy taken a step further ! Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted June 25, 2011 Author Share Posted June 25, 2011 "If this signal is not as equal as possible in all respects the defect will be compounded by the amplication factor of the output section. This equals big distortion numbers and generally bad sound." So this where the signal generator and scope come in? Off to a family reunion for me today. Boy am I gonna eat too much! Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 25, 2011 Share Posted June 25, 2011 at this point in the circuit you would use the function generator and scope to confirm proper phase inversion. The actual tuning of the circuit spoken of earlier will be done at the final output of the amplifier. Speaking of that I forgot to mention you will need a pair of 8 Ohm 20 watt minimum resistors to load the output for testing once we get to that point. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 25, 2011 Share Posted June 25, 2011 ( Quote ) I'm an ex drag racer from way back! My forum handle when I first stuck my nose into this loony bin was NOS440... Nitrous Oxide System and 440 cubic inches. Hence the reason my company name ended up NOS Valves but that Idea was born from the web page designer that first put together my website. For some reason I dont think the 440 was Mopar, I think it was Chevy taken a step further ! You have that right.... it was a 60 over big block chevy 427 which equals 439 cubic inches but I just rounded up. Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted June 25, 2011 Author Share Posted June 25, 2011 OK, made a little progress tonight. I got most of the resistors in. Waiting on the 47nf and the 1.5meg. All other resistors on the board have been replaced. Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted June 25, 2011 Author Share Posted June 25, 2011 I'll get the caps next. Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted June 25, 2011 Author Share Posted June 25, 2011 The last four solder joints for the evening before snipping the leads. I feel like its going pretty good at this point. I'm just taking my time. Craig, I got a couple of 8 ohm 25 watt resistors ordered also. If you see a problem in these pictures please just thump me on the forehead. [] Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted June 26, 2011 Author Share Posted June 26, 2011 Hey Craig, I want to run this by you to make sure I'm going in the right direction. On the Sectoral cap: Old New 50uf to 100uf 40uf to 100uf 30uf to 50uf 15uf to 50uf I'll install one on top witht the clamp and one underneath. I thought I would solder the two ground pins to ground circuit first and then work the Pos. Thanks. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 26, 2011 Share Posted June 26, 2011 OK, made a little progress tonight. I got most of the resistors in. Waiting on the 47nf and the 1.5meg. All other resistors on the board have been replaced. Hope that 47nF is a typo. That is if we are talking about the same small cap as previously the cap you need the 47pF not 47nf. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 26, 2011 Share Posted June 26, 2011 Hey Craig, I want to run this by you to make sure I'm going in the right direction. On the Sectoral cap: Old New 50uf to 100uf 40uf to 100uf 30uf to 50uf 15uf to 50uf I'll install one on top witht the clamp and one underneath. I thought I would solder the two ground pins to ground circuit first and then work the Pos. Thanks. By george I think you got it. The 17 years of fog is lifting [] Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted June 26, 2011 Author Share Posted June 26, 2011 Yep, that was just a typo. 47pf is what I ordered. Hope to get the transformers in the next day or two also. It would be nice to have those set for locating the JJ caps. Quote Link to comment Share on other sites More sharing options...
Tractrix Posted June 27, 2011 Share Posted June 27, 2011 Hey Craig, I want to run this by you to make sure I'm going in the right direction. On the Sectoral cap: Old New 50uf to 100uf 40uf to 100uf 30uf to 50uf 15uf to 50uf I'll install one on top witht the clamp and one underneath. I thought I would solder the two ground pins to ground circuit first and then work the Pos. Thanks. By george I think you got it. The 17 years of fog is lifting Be careful about making the DC supply capacitors too large since the inrush current may become so high that it strains the power transformer and rectifier too much. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 27, 2011 Share Posted June 27, 2011 Inrush lasts about 15 seconds.... way over stated. Prolonged over current is way more harmful then insrush current and if inrush was a problem a simple inrush current limiter would cure that. But really a 300uF total to charge up is nothing to worry about. Quote Link to comment Share on other sites More sharing options...
jtnfoley Posted June 27, 2011 Share Posted June 27, 2011 I don't remember reading the model number of this SC amp, but it looks like an ASR-120. Tom Bavis (IIRC) maintains the Made In Rochester site for SC stuff, and has the schematics and a bunch of sales literature for a BUNCH of Made In Rochester (NY) stuff: http://www.audiophool.cjb.net/MadeInRoch.html I have the SE little brother to this PP unit, the ASR110. Thinking about turning it into a 120 if I have the sockets for it as my next project. Needless to say, I'm reading this thread with great interest! Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted June 28, 2011 Author Share Posted June 28, 2011 Yes, this is the ASR-120. This same type amp is on Ebay this week. You might do better with buying one and refurbing it that way instead of a single ended to PP conversion. http://cgi.ebay.com/Vintage-Stromberg-Carlson-7408-tube-amplifier-VERY-NICE-/200616968209?pt=Vintage_Electronics_R2&hash=item2eb5b40011Craig, I just contacted Angela.com about my week old tranny order and they have one in stock and the other is apparently backlogged from Hammond. Bummer, so I cancelled that order. I then called to verify "in stock" and now have them ordered from Antique Radio Supply. Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted June 30, 2011 Author Share Posted June 30, 2011 Just to update where we are. The board is done with all new caps and resistors. Im thinking with the larger transformers blocking the old cap hole it might be best to go with both of the big caps under chassis as shown below. Are there noise concerns with the location of the caps? Supposed to have the transformers here from AES in the next day or two and will hopefully get it all together. Quote Link to comment Share on other sites More sharing options...
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