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Building ANOTHER DG-SE1 Amp!

Wharfcreek

Wharfcreek

Jack of all trades, master of none!!
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This build thread is for 'Take Two' of the DG-SE1 amp that Mr. Gillespie has so graciously shared with us. My first build is documented in a prior thread, but this one is going to show a bit more of the 'from' and 'to' aspects of what I'm doing....for anyone who's interested.

The project starts with one of two choices; either A) build the thing from 'scratch', or B) find a suitable 'donor'. Dave's original intents were to 'upgrade' the stock Magnavox 8604 to something of a respectable nature. However, in so doing, he actually created a 'project' amp that is easily built, not too costly, and performs amazingly well. But...that's all documented elsewhere. This project goes with selection 'B'....use of a 'donor amp'. In this case I chose a small SE-EL84 amp that I'd resurrected some time back. In the pics posted you'll note that it's NOT a 'Maggie' amp, but that it IS similar. It uses the same 4 tubes though I believe this was originally wired for a 12A'X' vs the 6EU7. I put the 'X' in parentheses as it don't know if it actually was an 'X', a 'U', a 'T', or what. But, in looking at the filament wiring, it's pretty obvious to me that it came that way...... I don't think I 'modified' it as I've done with some of the Maggie amps.

Anyway..... this post will end with the 'Donor' amp being photographed and shown in the pics below. BTW, I started this at about 9:30 am today, and it's now pushing 1:00. This, and the next post, are the progress made in about 3 hours of effort.

I also want to note 'why' I chose this amp as a donor: I spent some time yesterday doing some 'listening' tests between 4 of these little 'flea' amps. In looking at this unit, it clearly 'looks' as if it should be a great performer. The size of the OTs made me hopeful that it would FAR outshine the performance of the little Maggie. However....it actually sounded pretty lame. In looking underneath, you'll note that it's significantly different in design from the Maggie amp. And, the caps are OLD and probably shot. So, this amp made a great candidate for an overhaul. And, I'll now be able to clearly distinguish the change in performance as I have both my original DG-SE1 AND 2 OE 'Maggie' amps to compare this to. Should be interesting!
WC
 

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OK, moving right along, it took me a bit over an hour to 'gut' this amp! I was surprised to see that the multi-cap had a 1.5K resistor coupling the second and third stages. This is perfect for 'down the road' as per Dave's design. There was also a wire-wound resistor that coupled the first and second stages......so....that's where my 'dropping' resistor will go. I'll adjust my PS voltages from that point. However, the progress thus far will show the 'gutted' amp, the addition of a choke, the re-installation of the 2 new 8 ohm OTs, and some initial wiring. I'll also note that I had to move the PT back and over by about a quarter inch in order to make room for the choke. This took a little time, but turned out perfectly. Also, the choke had some plastic tabs I had to trim in order to get the outer section 'flush' with the front of the chassis. In mounting the OTs, the two share a single mounting hole where they 'butt' together. The original OT were just over-lapped at this point, but in my build I cut the tabs in order to have them meet 'flush' at the top of the chassis. No big deal....just a bit more time. I then used a screw, washer, and nut instead of the self-tapping sheet metal screws....just at this one point. I also had to trim a screw that was holding the choke on as it was a bit close to the PS section. Don't want any 'shorts' to chassis ground in ANY way!!

So, here it is now, PT repositioned, OT's mounted, choke mounted, OT's basically wired in, choke wired in, and only a cap left to install off the choke at the first stage of the PS. It's now 'break time'....and I'm off to lunch. 1:06PM..... not bad progress thus far!

WC
 

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OK.....made my first (caught) mistake. May be others I've NOT yet caught, but I did catch this one! So, for those of you looking, see if you can find Waldo ( a vestige of my kid's past where there was this game called 'Where's Waldo?' and he was buried into each page filled with TONs of minutia. A GREAT game to keep your kids occupied on a rainy day!!.....lol) Onward......
 
F, Derek has the OPTs correct, but my choke is one I had here. It's a Triad, and 1 Henry compared to the 1.5 in Dave's design. It's rated at 1500 volts and 60 ohms of resistance and 240ma. So, a 'suitable' substitute albeit not the exact one specified. But, as this is yet another 'donor' type project, I'm kinda using up stuff I have here. I'd also mention that my first stage of PS capacitance is 33uf at 450V, then to the off the choke to the first stage of the 3-section multi-cap....which is 60uf at 400V. So, I think I'll have good filtering. I'll chose the proper resistor to take the loaded voltage off that first stage and drop it to the 250 in the design, and then the 1.5K is already connecting stages 2 & 3....so, that should be correct from there out.

With this amp really being based on the OTs Dave used, at this point I'm still using new ones from AES as per Derek's link. I have 2 more sets on order.....one of which will actually go into a Maggie amp, the other.....not sure yet. I also have a complete set of iron from Edcor that I was going to use to build Redboy's 'Dolly' amp. However, in looking at this design from Dave, I think I'll do a complete 'chassis up' build using that iron and Dave's schematic. We'll see how that works out. Anyway...back to it.

Find Waldo yet?

Tom
 
well I just sprung for a Barter town 8601 minus tubes
just the trik for what I want to do and now no worries on PT or OPTs.
Will get what derekva is using. I have all tubes needed. Looks like this will happen sooner than expected.
 
F, Derek and I are both using the OPTs that Dave specified. These are a 'no-brand' version of something....but Dave scoped 'em out on Antique Electronic Supply, and I found the same ones on CE Distribution's site (they're related companies, so 'duh'!!). You will need to order the two OTs for about $30 and the one Choke for another $15 or $20 or so. Beyond that, I suggest you go over the schematic and make a list of your passive parts, and be aware that you CANNOT go buy these at Radio Shack (or damn near anything else 'electronic' these days). You'll either have to add passive parts to your AES order, go to Mauser or Digikey, or find a local store that really DOES sell electronic parts!

Good luck with your build! I'm back to my 'Take 2' project. Just a few more parts to solder in and I'll be ready to start checking 'loaded' voltages. With luck, I'll be taking it for a test ride before the sun goes down.

Tom
 
well I have a fair ta middlen bunch of Rs and Cs from doing a bunch of other refurb/restoes on several amps and preamps so I think I probably have all I need. But when I order the OPTS and choke I'll get anything I am shy on.
As I see it this will be a strip all old parts and replace with the DG parts.
thats cool cause it lets me drop all the sockets to do a bang up job on the chassis for a nice looking finish, either paint or just burnushed steel chassis. Some side wood strips will look good as well.
 
OK, update on my #2: Seems once again I have PS voltage problems. Only this time , I'm looking at too little vs too much. I had built this in the following manner from the output of the rectifier tube: CLCRCRC with the following values: Choke is 1H with 50 Ohms resistance and first stage cap is a 33uf-450V axial I added from the rectifier output to ground ahead of the choke, The output of the choke is going to the first of 3 sections of the multi-cap being an 60uf at 400V. I now have a 10 ohm resistor connecting the next stage, which is a 40uf @ 350V, then 20uf @ 300V with a 1.5K connection in between. I've got the OPTs connected AFTER the 10 ohm resistor and at the 40uf section.....and at that point I'm measuring about 240V. I tried a 1 ohm resistor and voltage actually dropped some. And, if I remove the first section completely, take the 33uf-450 OUT of the circuit, connect the choke between the first and second sections of the multi-cap.....voltage drops down to about 200V. So, clearly.....PS needs some 'tweaking'. Any suggestions would be appreciated!! TSD
 
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What's the PS trans specs?
Maybe buck it up instead of down then use resistors to adjust the heater V. Some on these Forums seem to think less DCR in the PS results in better sonics (dynamics) so maybe try taking the choke out (they recommend if a choke is used it's R be about 20 ohms or less and no other R's be used before the B+ to the output transformer) Anyways you can now maybe experiment to see what you think!
 
Tom,,
Seems like a lot of resistance on the choke you have,, resistance of the choke speced is only 56 Ohms, thats probably your discrepancy...
 
Pulled the multi-cap and tested it. According to the Tel-OMike tester, it's OK. I also did a uf check in the little hand held unit....and seems pretty close. The 60uf section is like 63uf, the 40uf section is like 36, and the 20uf section is like 18. Leakage numbers on the TelOMike are well below minimum. So, that doesn't seem to be it. Did some further testing, and seems that with tubes OUT, I can get about 350V showing at the B+ connection to the OPTs. But, as soon as OPTubes are reinstalled (even without the driver tube), the voltage is dropping by over 100 volts....from like 350 to 230 or 240. This seems like WAY too much voltage drop just from tubes. So, any thoughts? WC
 
John, did you mis-read that post as 600 ohms on the choke? If so, I can understand. I should've had a space in there. But, choke is actually 50 ohms, not 60. So, I misinformed you altogether.(note: above post corrected from 60 to 50 and space added after numbers.) Thanks John!

I'm going over my 'build' now.....to see if I erred anywhere.....or perhaps have a wire with a insulation short. And, maybe it's just my tubes? In any event, I have to solve this or the day was a waste! WC
 
My bad John! But, now corrected in the post. Wish finding the amp's problem was as easy!! Tom
 
I may have missed it, how does the PT match up to the one in your 1st amp? Same one? If not, is it possible the 2nd amp PT is smaller?
PS.. If the PTs are the same, maybe try the tubes from the 1st amp, to see if the tubes may be drawing more current...
 
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Tom -- What is the AC voltage that the PT is delivering to pins 1 and 7 of the rectifier tube with the output tubes installed and drawing current? The original Magnavox transformer delivers about 235 - 237 vac under that condition to deliver the listed B+ voltages.

Dave
 
Actually showing more than that. "Loaded" I'm seeing about 260 each side from the CT (which is grounded to the chassis) About 525 across the two. So, something isn't lining up here...... WC
 
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