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D150 monster amp and funny tooobz
D150 monster amp and funny tooobz
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Old 18th November 2018, 09:40 AM   #11
Eli Duttman is offline Eli Duttman  United States
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Koja, touch base with Jim McShane, as you do your refurb. He's both very knowledgeable and honest. If you need new O/P tubes, there is a bit of a conundrum. Really good 6550s are not currently being manufactured. IMO, the "best" replacement you can currently obtain is the "reissue" Gold Lion KT88. If, as is ARC's pattern, 1 or more big tubes are being used as screen grid regulators, a less costly variant (such as the EH KT88) can be used in that/those position(s).
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Old 18th November 2018, 01:39 PM   #12
koja is offline koja  Canada
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Thanks for the contact. All info is welcome as I am a newbie to tubes. I am still hoping that all tubes will be functional. Naturally I had to remove them all so that I could take the amp apart. I see that all O/S tubes have been numbered presumably when they were paired by measurements. I wrote down all positions so they go back to the same sockets.

This amp has been built like a tank, but boy they sure did not have serviceability in mind when they did the tight layout. Plus with 134lbs weight this thing is a 2 man job to flip around, especially when it comes to pieces and can no longer hold together. I had a friend help me do all the flips to get to the screws in a manageable order. I am lucky he is an electronics professional and had real sense to figure this one out. We left transformers alone which made flipping the boards connected just with wire harnesses a challenge.

Here is what I was trying first to get to, the big electrolytic caps on the back board and under the unit.
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File Type: jpg D150_open_230006_r.jpg (185.9 KB, 468 views)
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Old 18th November 2018, 01:58 PM   #13
mctavish is offline mctavish  Austria
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More Pics!!! This is a tube legend!

I would love to get my hands on one of these... Thanks for documenting this. Hopefully those GE 6550's are still good, they are great tubes in my experience..
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Old 18th November 2018, 02:08 PM   #14
tsmith1315 is offline tsmith1315  United States
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Quote:
Originally Posted by koja View Post
I am a newbie to tubes.
Well, that's one hell of an amp to start out with!
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Old 18th November 2018, 02:18 PM   #15
mctavish is offline mctavish  Austria
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Amen to that.

Like sayin' "I'm new to cars", and starting by restoring a lamborghini Miura!

I cant wait to see it up and running!!
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Old 18th November 2018, 11:57 PM   #16
koja is offline koja  Canada
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I know about "the legend" part, less than 200 made. But like I said, D150 really wrecked my plans since in this audio system I have all balanced signal gear including these class A mono blocks:

Burning Amp BA-3b (Balanced)

So it is just a curiosity on my part that I will try it for a while. I think in a couple of years someone will luck out and get an amp which will be made to run for another 40 years .

As a matter of fact, people were telling me "Do not mess with it. there are vintage nuts out there who will pay more for it in its original condition etc.". But I let that boat sail since I am too much into amps to settle for anything less than the best performance possible if I am going to try it.

All power supply caps are being changed with these:
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File Type: jpg Vishay_cap_forD150refurb.JPG (110.0 KB, 427 views)
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Old 19th November 2018, 12:11 AM   #17
rayma is offline rayma  United States
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Quote:
Originally Posted by koja View Post
D150 really wrecked my plans since in this audio system
I have all balanced signal gear
You can easily convert the D150 to full balanced operation,
and it will sound much better that way.

You can remove the unity gain polarity inversion stage (V1 and V2),
as the inverter is outside of the overall negative feedback loops.
Feed the balanced inputs directly to the 12AX7 input amplifier (V3 and V4) grids,
via the 10k resistors R12 and R15.

The rest of the circuit is balanced, including the output transformer
secondary and feedback loops.

Last edited by rayma; 19th November 2018 at 12:26 AM.
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Old 19th November 2018, 12:20 AM   #18
koja is offline koja  Canada
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These are the original caps being replaced: the rear board features 8 x 200uF and the PS at the bottom 12 x 600uF.

they are all being replaced with 20 x 820uF. So the back board gets four times as much capacity and the bottom gets more capacity in half the length (thanks to the advances in cap technology since 1975).
Attached Images
File Type: jpg D150_RearBoardCleaned_092719_r.jpg (387.8 KB, 387 views)
File Type: jpg D150_RearBoardCap_195206_r.jpg (282.1 KB, 365 views)
File Type: jpg D150_PSCaps_230105_r.jpg (176.1 KB, 372 views)
File Type: jpg D150_PScapsOriginal_183937_r.jpg (213.6 KB, 192 views)
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Old 19th November 2018, 12:26 AM   #19
koja is offline koja  Canada
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Thanks Rayma. I will look into it. If you guys continue supporting me like this I may just end up making a servo to get read of the variac and the adjustments and keep the damn thing (that is IF it makes it by my better half; I will even have to have a new TV stand made just to bring that thing into the room ). like I said: my friend going to the auction wrecked a perfect plan.
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Old 19th November 2018, 12:28 AM   #20
rayma is offline rayma  United States
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Quote:
Originally Posted by koja View Post
I will even have to have a new TV stand made just to bring that thing into the room ).
ARC used an engine hoist to move the D150s around at the factory.

Last edited by rayma; 19th November 2018 at 12:51 AM.
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