Rebuilding extremely early 700, would love input and assistance.

Saabracer23

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#1
Some may remember a thread I posted a little while back trying to figure out what amplifier I had exactly. It belongs to a buddy and he wanted me to White Oak it, but we found through the help of this forum that it’s one of the earliest 700s (only 16 outputs) that was put out and from the Seattle location as well. So I’m just going to rebuild it so that it can be used and he is going to find a different 700 to White Oak.

First off, from my understanding there were only a handful of these 700s that left in this configuration, any chance of finding a schematic or service info?

Ive replaced all of the electrolytics except the main filters, waiting on White Oak to get some in stock. Is there anything else on the main board that should be replaced? Any transistors that should be swapped out? I see that each channel has and RCA 40327 and MM4003 metal can transistors. Should I just leave them be or swap them out? I have plenty of the 2N3440 and 2N5416. I see the suggested replacement is the 2N5415, but the 5416 should work fine correct? I was also thinking of changing out the 6 trimmers, 2 for input offset, 2 for output offset, and the other 2 I assume are bias. Any tips on adjusting these would be awesome. I’d think output offset would be the standard practice of measuring at the output and adjusting for zero


I also see each channel as a pair of RCA 40396P germanium transistors. Germaniums can be tricky when looking for equivalents.

Now for the outputs. Most of the outputs are shorted, it’s an odd arrangement of parts. My plan was to throw 16 new MJ21194G or MJ21196G in there since all 16 now are currently NPN devices.

Well then Grapplesaw said this to me in a PM:

So Dan you only need 12 96g’s for that amp if you leave it quasi complementary. Re use rage race 410’s in the first row or use 4 mj21195’s there.

Maybe that’s why it has shorted outputs? There need to be 4 PNP devices. Where do these four devices go exactly? It’s currently filled with 2SD555s and devices with absolutely no markings whatsoever. Measuring the ones that are not shorted has shown there is not a single row or column that has a PNP device. Anyone point out what I should put where as far as the outputs are concerned?

3505C8CD-6714-4DEF-96C3-9BFD394F7DAE.jpeg
58BC96E6-6937-455F-AD9B-3F38CE7B9D67.jpeg
8DAB94C0-E93F-4800-9E73-CFA24479EE5B.jpeg

Thank you,
Dan
 

Gepetto

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#2
Some may remember a thread I posted a little while back trying to figure out what amplifier I had exactly. It belongs to a buddy and he wanted me to White Oak it, but we found through the help of this forum that it’s one of the earliest 700s (only 16 outputs) that was put out and from the Seattle location as well. So I’m just going to rebuild it so that it can be used and he is going to find a different 700 to White Oak.

First off, from my understanding there were only a handful of these 700s that left in this configuration, any chance of finding a schematic or service info?

Ive replaced all of the electrolytics except the main filters, waiting on White Oak to get some in stock. Is there anything else on the main board that should be replaced? Any transistors that should be swapped out? I see that each channel has and RCA 40327 and MM4003 metal can transistors. Should I just leave them be or swap them out? I have plenty of the 2N3440 and 2N5416. I see the suggested replacement is the 2N5415, but the 5416 should work fine correct? I was also thinking of changing out the 6 trimmers, 2 for input offset, 2 for output offset, and the other 2 I assume are bias. Any tips on adjusting these would be awesome. I’d think output offset would be the standard practice of measuring at the output and adjusting for zero


I also see each channel as a pair of RCA 40396P germanium transistors. Germaniums can be tricky when looking for equivalents.

Now for the outputs. Most of the outputs are shorted, it’s an odd arrangement of parts. My plan was to throw 16 new MJ21194G or MJ21196G in there since all 16 now are currently NPN devices.

Well then Grapplesaw said this to me in a PM:

So Dan you only need 12 96g’s for that amp if you leave it quasi complementary. Re use rage race 410’s in the first row or use 4 mj21195’s there.

Maybe that’s why it has shorted outputs? There need to be 4 PNP devices. Where do these four devices go exactly? It’s currently filled with 2SD555s and devices with absolutely no markings whatsoever. Measuring the ones that are not shorted has shown there is not a single row or column that has a PNP device. Anyone point out what I should put where as far as the outputs are concerned?

View attachment 51553
View attachment 51554
View attachment 51555

Thank you,
Dan
No PNPs in there please...it is quasi comp.

Use RCA410s in column 2 and 4 (count starting from the transformer) in the bottom row only. You will need 2 such devices. Everything else should be MJ21196
 

Saabracer23

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#3
No PNPs in there please...it is quasi comp.

Use RCA410s in column 2 and 4 (count starting from the transformer) in the bottom row only. You will need 2 such devices. Everything else should be MJ21196
Thank you for the feedback. So here are the columns as the sit.

From the transformer here are 1 and 2:
6CFFA390-85D7-4027-9FBB-F2942BAE4FD7.jpeg

And here are 3 and 4:

CEBA190B-4658-4283-B772-7D43CF74C2C0.jpeg

You can see that in all of 1 and 2 they are all 2SD555 with the exception of two. The two in the very bottom row are blank.

In column 3 and 4 every single device is blank. Who would put completely blank devices in this unit?!?!

Here are the 3 I pulled in order from right to left being from column 1, 2, and 4

D73F7AAB-E8D1-4E9C-A38F-3F8878AF3612.jpeg

For outputs, the 21194 and 21196 appear to be equal, so I’m assuming I could use either. The 96 seems to be the go to here. I just have more MJ21194 (around 90 each 21193G/21194G vs around 60 each 21195/21196).

So I need to find 2 driver then for the 2 RCA 410s. There is literally no way to tell if any of these blank units are 410s. I’ll look through my stock, maybe I pulled some from something else.

If not, what are my options? I’m not a huge fan of buying from eBay. Are there equivalents? I have a bunch of MJ15024, MJ15003, MJ15015, MJ802, and others. Any suggestions?

Dan
 

Gepetto

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#5
MJ21196 have a better SOA spec than the MJ21194. That is a primary difference. No Hfe matching required, that is what emitter resistors do. Use the same date code if you can, the matching within a date code lot is excellent.
 

Gepetto

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#6
You basically have a PL400 with a PL700 transformer mounted on it. You won't be able to achieve reliable full power output which is what PL also discovered, thus the 2 extra transistors added per column in the follow on, production PL700s
 

Saabracer23

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#7
You basically have a PL400 with a PL700 transformer mounted on it. You won't be able to achieve reliable full power output which is what PL also discovered, thus the 2 extra transistors added per column in the follow on, production PL700s
Yeah, that’s what I figured they figured out. So I found that the “blank” ones do have writing on the sides of the case. They say “PAT 3242555 FB” and at the very end I think it says 38. They’re all pretty warn.
CBBDFE47-9EF2-4DA0-9A08-0AD0ED5622F2.jpeg
Since the numbers end in 2555, I’m guessing they are some form of the 2SD555????

Any suggestions on a suitable replacement for the RCA410? The amp clearly doesn’t have any on it currently. I’d hate to have to go to eBay to source them. Just worried about fakes. Plus not having to wait on anything to ship would be a plus!

Dan
 

Gepetto

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#8
Yeah, that’s what I figured they figured out. So I found that the “blank” ones do have writing on the sides of the case. They say “PAT 3242555 FB” and at the very end I think it says 38. They’re all pretty warn.
View attachment 51562
Since the numbers end in 2555, I’m guessing they are some form of the 2SD555????

Any suggestions on a suitable replacement for the RCA410? The amp clearly doesn’t have any on it currently. I’d hate to have to go to eBay to source them. Just worried about fakes. Plus not having to wait on anything to ship would be a plus!

Dan
555 transistors are not very good devices when compared to modern tech. If I had a pair of decently matched 410s I would give them up but they are radically different so think that one or more are walking wounded devices. Others on this forum may have some from pulls made during upgrade. My parts mules have an Easter egg assortment like yours does.
 

Saabracer23

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#9
555 transistors are not very good devices when compared to modern tech. If I had a pair of decently matched 410s I would give them up but they are radically different so think that one or more are walking wounded devices. Others on this forum may have some from pulls made during upgrade. My parts mules have an Easter egg assortment like yours does.
That is very kind, I appreciate the offer. I’m guessing that there isn’t a equivalent to the 410?

Dan
 

Saabracer23

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#12
I went ahead and replaced the MM4003 and 40327 pairs. I pulled them and the pair on the left channel were measuring with an hFE of around 40 each and the right they were around 170 each. I matched some (I know they don’t need to be) and put them in.
111F2BD1-D44E-4B5C-B5FB-B70FD7919DFD.jpeg

Would it be wise to pull the germaniums? I know that by nature they are leaky, anyone ever run into bad ones?

Dan
 

laatsch55

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#13
I doubt you'd ever find replacements....test for shorts in circuit and call it good..
 

Saabracer23

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#18
I’ve been waiting sometime for White Oak to get the filter caps in stock, they emailed me and I now have them, thank you White Oak! I feel the pain, parts are getting scarce, Mouser just shorted me almost half my order of items that said were in stock when I placed the order, now those parts aren’t to be shipped until late November.

Anyways, I’m going to be finishing up this project and my buddy, the owner had a question. So I told him that with this being an early 700 that it wouldn’t be as stable as a standard one and that he probably shouldn’t drive it too hard.

He wanted to know how it would do with a 4 ohm nominal load, Klipsch Palladium P-38 towers to be exact. That’s a pretty nice speaker and I’m not sure if it’s best to trust this amp with them. I told him I’d ask though.

Thank you,
Dan
 

MarkWComer

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#20
Still curious if anyone has thoughts on this amp driving some 4 ohm speakers.

Dan
I walk away from 4Ω speakers. I’m sure there are very nice ones, but I just don’t like low impedance speakers for the possibility of overheating and burning my outputs. This is something to think about with this amp due to the oddity of the design.

I have a pair of Cerwin Vega VS-12 connected to a Pioneer SX-780 with darlington outputs. The amp is 50wpc, so I connected a 4Ω 50watt non-inductive resistor in series to raise impedance to 8Ω. Of course, you will need something larger than a 50w resistor for your amp. (Apologies for the crummy picture…) 033CEB21-8CC5-4FDA-9A0E-11569E89F9BF.jpeg
 
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