CECAA850 Posted December 12, 2016 Share Posted December 12, 2016 31 minutes ago, JL Sargent said: Now as to me hearing the difference? 20 concerts, chainsaws, firearms, dirt bikes, and fire crackers all say its a miracle I can hear at all. Certainly glad you can hear. I guess my ears aren't golden either as I've tried to hear the differenced between the two connections and never could. I could definitely hear a difference using the plate amp's high level outputs but no real difference between SQ in high level and low level inputs. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 16, 2016 Author Share Posted December 16, 2016 So far. Everything seems fine with the iron regarding measurements of resistance and inductance... The holes I had previously drilled for binding posts were too far spaced apart for the ones I purchased. So I had to get creative with nylon bushings and washers, to use the binding posts I had bought. A bit of a chore. I mounted test point jacks to measure bias voltage for each pair of 6BQ5/EL84. One post was too long, and the test jack was too tall. I had to shorten both for clearance. Now that hassle is over, I can start wiring/layout. That's the fun part of working on old console amplifiers, with existing drilled holes. Mike Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted December 16, 2016 Share Posted December 16, 2016 Mike, in with Orange Drops this time or do you have another cap in mind? Quote Link to comment Share on other sites More sharing options...
avguytx Posted December 16, 2016 Share Posted December 16, 2016 I used the 716p Orange Drop caps in mine....and in the S/C ASR-120, too. Hard to beat for the money. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 16, 2016 Author Share Posted December 16, 2016 Yes, I'll be using the 716P orange drops. They are hard to beat for the money. 716P is a polyprop with tinned copper leads, epoxy dipped, and small enough in size to work in most projects. Great for vintage console amplifier budget gear. The retired EE audio mentor friend always said to save those fancy exotic coupling caps for the single-ended amplifiers. If there is a difference in sound quality from a fancy coupling cap, it will be more than likely be noticed through a simple circuit such as a single-ended tube amplifier. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 20, 2016 Author Share Posted December 20, 2016 Power supply transformer all connected using the extra 7 volt heater winding for bucking the secondary to a lower voltage, along with a fuse holder and power switch. The B+ positive wire from the rectifier socket has been switched from pin 2 to pin 8, for use of a 5AR4 or 5V4GA. The original 5U4 taps B+ from pin 2...dunno if it matters which pin, but the pin-outs show pin 8 for these type of indirectly heated rectifiers. Moved the CT for the PS xformer to the can cap ground...a good practice in my opinion. The three section capacitor with the choke connected...1st cap 40uF, choke, 2nd cap 40uF for the B+, 10uF for the 6BQ5 screens, and 40uF for the 6EU7s. I goofed and could have used a higher capacitance cap for the screens, but 10uF will be satisfactory. Gillespie mentions when using more capacitance (like 40-50uF) for the screen grids of the 6BQ5s, to use 100 ohm stability resistors at each screen grid. I went ahead and installed them in the likelihood the multi-cap would eventually get replaced for a new 40uF four section cap. That would eliminate a tag strip... From the 10uF cap for the 6BQ5 screens, a 330K resistor inputs to a 5K pot and powers the negative regulator at the adjustment pin. The one side of the 5K pot is grounded through a 15K resistor. The input pin is grounded, and the output pin goes to a pair of 10 ohm sensing resistors, each resistor will be connected to one pair of output tubes. The test points will be connected with left/right tests points connected at each 10 ohm sensing resistor, and the common test point at where each 10 ohm resistor meets at the regulator output pin. The two 220 ohm resistors from the 6.3 volt winding to the output pin of the regulator serve some sort of regulation as well...it escapes me at the moment as to exactly how... Now to wire up the 6EU7s, coupling caps, feedback and speaker outputs. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 23, 2016 Author Share Posted December 23, 2016 Just need to finish the feedback connections, run the wiring for the cathodes and test points, connect the binding posts, the RCA jacks/wiring, then B+ to the OPTs. Scrounge up some tubes, and see if the voltage/current matches up with Gillespie's schematic...heh 2 Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted December 24, 2016 Share Posted December 24, 2016 Heck, you'll be listening in no time! Quote Link to comment Share on other sites More sharing options...
avguytx Posted December 24, 2016 Share Posted December 24, 2016 That's pretty sassy looking under the hood. Very nice! Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 28, 2016 Author Share Posted December 28, 2016 Just need to dig out the tube caddy and find some 6BQ5s, and a few more 6EU7. Then the magic smoke test... Darn, a crooked feedback wire... Quote Link to comment Share on other sites More sharing options...
mike stehr Posted December 28, 2016 Author Share Posted December 28, 2016 Scratchy shiny Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 1, 2017 Author Share Posted January 1, 2017 Everything measures up with the Gillespie modded Magnavox 9300 schematic voltage-wise. My only issue right now is a pair of matched 6EU7. I don't have a decent matched pair to get the plate voltage even. I have one 6EU7 that will match the target 185 plate voltage for each plate, but the others are ten volts lower, or ten volts lower on one plate, 6 volts lower on the other...argh...the close as I can get is a 6EU7 with 176 and 179 on each plate. So I'll need a Sovtek 5AR4 rectifier, (using a Mullard GZ34 for now) and some new or NOS 6EU7...Sovtek? Almost there...however, I probably can listen to it with the tubes I have in the amplifier. Pay no heed to the blue painters tape with random numbers written upon them. Quote Link to comment Share on other sites More sharing options...
davesans Posted January 1, 2017 Share Posted January 1, 2017 Very nice work there looks great. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 2, 2017 Author Share Posted January 2, 2017 I took a look at a 2kHz square-wave for each side of the amplifier, and the waveform is pretty close to Gillespie's scope pics of the 2kHz square-wave in his AK Magnavox 9300 mod thread. I have a little more of a peak on the top left edge as compared to the AK thread image, but not by much...and I really need to invest in another function generator. The amplifier and or pot in this Simpson 420 is so dodgy, that I can't really much depend on the voltage/waveform it's putting out anymore. I run the function generator directly to the scope, and if slightly touch the amplitude pot the waveform on the scope comes unglued, until I noodle with the pot or leave it turned down...rats... I planned on listening to the amplifier tonight, but there is a nice blizzard with 35-40mph+ winds. I really don't want to lose power in the middle of a listening session. Mike Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted January 2, 2017 Share Posted January 2, 2017 Looks terrific Mike! What did you use to get the beautiful finish on the chassis? I used to do them by hand with Mother's Aluminum Polish, but decided that it is too much work! Maynard 1 Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 2, 2017 Author Share Posted January 2, 2017 4 hours ago, tube fanatic said: Looks terrific Mike! What did you use to get the beautiful finish on the chassis? I used to do them by hand with Mother's Aluminum Polish, but decided that it is too much work! Maynard Mother's Aluminum Polish works well with metal as well. The first time I worked on the amplifier back in 2003 I sanded the chassis a bit by hand when it was torn down and polished it with Never Dull if I recall. This time around it just took some light sanding and polishing. Nonetheless, it is a lot of work and I wouldn't condone sanding those cadmium coated chassis'...it's probably not the most healthy thing to do without proper ventilation, gloves, etc... About 2 months and it will tarnish back to the way it was. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted January 2, 2017 Author Share Posted January 2, 2017 It works, and sounds rather nice. Better than I expected. I personally think these modifications make the amplifier sound better than stock form, or other modded variations. It's been some time since I listened to the amplifier in original form, but I don't ever recall it sounding this good. A good balanced overall sound with the Cornwalls, with I'm pretty certain better bass response. Not bad for a puss-pull amp. Maybe because it's pretty much powered by Mullard... 1 Quote Link to comment Share on other sites More sharing options...
avguytx Posted January 3, 2017 Share Posted January 3, 2017 I need to get me one of those "puss-pull" amps! ;-) Quote Link to comment Share on other sites More sharing options...
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