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Old 1st January 2021, 08:00 PM   #2621
drbabe is offline drbabe  United States
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Join Date: Dec 2020
Location: Pennsylvania
Question Trying to find history of my Acoustat Tube Amps

Greetings

I'm a new member to this forum and joined because this is one of the only places I found that discusses Acoustat products.

I've owned a pair of 2+2's and Acoustat "servo amps" since 1985.

I'm trying to understand the history of my amps, without reading thru 262 pages of posts .

My Amps are marked Acoustat Model X, Serial # 1691 and 1692. When I originally got them they had oil filled coupling caps that went straight to the panels. From what I understand, they were not stock models, they had been modified by David Curcio. From what I could see, that had separate regulators for the Screen suppy of the 6HB5's and a reguator for the B+ of the 6DJ8 drivers.

In the early '80's I became friends with Danny Fanny (founder of American Hybrid Technology...now defunct) and he made some additional mods...changed some components, most notably got rid of the oil filled caps and replaced with polystyrene caps or polypropylene..not sure, and most recently, just before the pandemic hit, some additional mods. Mainly replacing the caps and resistors in the signal path.

I also understand from reading here there are also "Medallion Transformers" to drive the Panels. Are these a stand alone interface to bias panels? Do they also have an Acoustat Tube amp that drives that interface? Do you supply your own conventional amp (either valve or solid state)?

What came first, the Transformer or my Servo Amps?

TIA for any answers.

ps..I am totally happy with this system, I do have it set up in a Dead End, Live
End type of room and it is a pleasure to listen to.

Last edited by drbabe; 1st January 2021 at 08:06 PM.
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Old 1st January 2021, 08:09 PM   #2622
moray james is offline moray james  Canada
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Join Date: Aug 2003
Location: Calgary on the Bow
Quote:
Originally Posted by artm View Post
Quick question: in a 1+1, if a top panel is making a rattling sound, would that indicate a panel issue or an interface one (transformer)?

Does the top panel handle only highs (by one transformer) or are both fully driven?
all panels run full range. if a panel rattles it has a problem could be the panel is loose could be that some of the stator panels have broken loose could be the diaphragm has lost tension and is fluttering can make a lot of noise. You are going to have to take them apart and have a very detailed look and come back when you have something to report.
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Old 1st January 2021, 09:51 PM   #2623
OldMovieNut is offline OldMovieNut  United States
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Join Date: Jan 2013
Location: Fort Wayne, Indiana
Quote:
Originally Posted by drbabe View Post
Greetings

I'm a new member to this forum and joined because this is one of the only places I found that discusses Acoustat products.

I've owned a pair of 2+2's and Acoustat "servo amps" since 1985.

I'm trying to understand the history of my amps, without reading thru 262 pages of posts .

My Amps are marked Acoustat Model X, Serial # 1691 and 1692. When I originally got them they had oil filled coupling caps that went straight to the panels. From what I understand, they were not stock models, they had been modified by David Curcio. From what I could see, that had separate regulators for the Screen suppy of the 6HB5's and a reguator for the B+ of the 6DJ8 drivers.

In the early '80's I became friends with Danny Fanny (founder of American Hybrid Technology...now defunct) and he made some additional mods...changed some components, most notably got rid of the oil filled caps and replaced with polystyrene caps or polypropylene..not sure, and most recently, just before the pandemic hit, some additional mods. Mainly replacing the caps and resistors in the signal path.

I also understand from reading here there are also "Medallion Transformers" to drive the Panels. Are these a stand alone interface to bias panels? Do they also have an Acoustat Tube amp that drives that interface? Do you supply your own conventional amp (either valve or solid state)?

What came first, the Transformer or my Servo Amps?

TIA for any answers.

ps..I am totally happy with this system, I do have it set up in a Dead End, Live
End type of room and it is a pleasure to listen to.
The amps are from the first Acoustat speaker, the X. The next generation of speakers, the Monitor 3 and 4 also had direct drive tube amps. All. subsequent generations used transformers where the user supplied an amp of their choosing.
Someone replaced the transformers with the amps from an X, Monitor 3 or 4.

Cheers,
OldMovieNut
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Old 4th January 2021, 07:53 PM   #2624
Discopete is offline Discopete  Canada
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Join Date: Nov 2009
Wondering if anyone can advise on power rating for volume and tone pots on the DD Servo OTLs. They're a bit scratchy and I want to replace them. Right now they are 1watt pots. Available quality upgrades are quite a bit lower in rating, like typically 1/4watt. How critical is it? TIA
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Old 22nd January 2021, 04:05 AM   #2625
Mikerodrig27 is offline Mikerodrig27  United States
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Join Date: Aug 2014
Location: Cape Coral, FL
Hi, I have made some ?progress? on my Spectra 11's that I had posted about over on #2460

I did the power supply update which did bring the bias up a bit but not enough. one of the speakers will get up to a bias of roughly 44v the other to about 62v. I have tried many things. I replaced the input diodes, the diodes on the HV side, the transistor, replaced the zener diode with a 13v, I did the update and checked all of the other components on the board to see if they are within spec, swapped the wall warts from speaker to speaker. I feel like I am running out of options.

The only components that I haven't checked are the high volt ceramic caps, the large 500m resistor on the high volt side, the ceramic caps, the 10m resistor that the grey wires go to ground from. I even pulled off the trimmers and checked if they were good.

From what I understand, ceramic caps rarely go out. I have a LCR meter and may pull a couple off and see what the ESR is on them. Can I pull them out of the circuit and see if that changes the bias? Also, is it worth it to try to change the large 500m resistor?

I noticed that the voltages are higher on the low volt side of the power supply that has the lower bias. I can only assume that is because the little wall wart transformer doesn't have enough of a load on it to pull the voltage down.

I may try cleaning the ground wire connection to see if that helps before I go digging into the power supply further than I already have. If I can figure out this issue, the interface will pretty much stuffed with all new parts throughout!
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Old 22nd January 2021, 09:12 PM   #2626
Atom666 is offline Atom666  Canada
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Join Date: Oct 2005
Location: Toronto, Canada
Quote:
Originally Posted by Discopete View Post
Wondering if anyone can advise on power rating for volume and tone pots on the DD Servo OTLs. They're a bit scratchy and I want to replace them. Right now they are 1watt pots. Available quality upgrades are quite a bit lower in rating, like typically 1/4watt. How critical is it? TIA
Try some Nu-trol control spray cleaner for the pots. Give them a shot of the cleaner in the openings where the 3 terminals are. Power off of course;^)
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Old 22nd January 2021, 10:55 PM   #2627
Discopete is offline Discopete  Canada
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Join Date: Nov 2009
thanks. I have deoxit but these are now 40 years old. I bought some new ones. I have 3 pairs of these amps and I'm noticing they vary in the action of the pots in that one may feel smooth while another feels like a spike digging and dragging as I turn it. Time to change them

These are very nice with great specs
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Old 23rd January 2021, 10:42 AM   #2628
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Location: Chandler Arizona
Quote:
Originally Posted by Mikerodrig27 View Post
Hi, I have made some ?progress? on my Spectra 11's that I had posted about over on #2460

I did the power supply update which did bring the bias up a bit but not enough. one of the speakers will get up to a bias of roughly 44v the other to about 62v. I have tried many things. I replaced the input diodes, the diodes on the HV side, the transistor, replaced the zener diode with a 13v, I did the update and checked all of the other components on the board to see if they are within spec, swapped the wall warts from speaker to speaker. I feel like I am running out of options.

The only components that I haven't checked are the high volt ceramic caps, the large 500m resistor on the high volt side, the ceramic caps, the 10m resistor that the grey wires go to ground from. I even pulled off the trimmers and checked if they were good.

From what I understand, ceramic caps rarely go out. I have a LCR meter and may pull a couple off and see what the ESR is on them. Can I pull them out of the circuit and see if that changes the bias? Also, is it worth it to try to change the large 500m resistor?

I noticed that the voltages are higher on the low volt side of the power supply that has the lower bias. I can only assume that is because the little wall wart transformer doesn't have enough of a load on it to pull the voltage down.

I may try cleaning the ground wire connection to see if that helps before I go digging into the power supply further than I already have. If I can figure out this issue, the interface will pretty much stuffed with all new parts throughout!
Are you measuring the bias voltage with speaker disconnected? If not, and one of the panels has a bias leak, it could be pulling down the bias.

My next suspicion would be the capacitors in the high voltage multiplier. These are pretty reliable, but your speaker is already 30-ish years old, and at this point, one must be suspicious of all components. Be sure to replace all of them at once, using the same type, capacitance and voltage value. Here's a recommended replacement diode and capacitor:

Vishay GP02-40 diode, 250 mA, 4000 volts
Mouser p/n 625-GP02-40-E3

Vishay 564R30TSD33 capacitor, 3300 pF, 3000 volts
Mouser p/n 75-564R30TSD33

My next step would be the 500M-ohm resistor. You can't measure its value with a conventional ohmmeter, so you could try swapping parts between interfaces as a troubleshooting step.

Any fault in the 10M-ohm resistor should should not affect your bias readings.

Good luck!
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Old 23rd January 2021, 01:52 PM   #2629
Mikerodrig27 is offline Mikerodrig27  United States
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Join Date: Aug 2014
Location: Cape Coral, FL
Thank you for your reply. I was testing both with the panels disconnected and then with the panels connected (letting the interface run for 24hrs)

I have already replaced the HV diodes and will go ahead and try the HV multiplier caps next.

Also, do you have a good recommendation for replacing the 500m resistor?

Thanks for your reply!
Mike
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Old 24th January 2021, 09:45 PM   #2630
hhhh is offline hhhh  Canada
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Join Date: Oct 2007
What is the purpose of the single wire that comes out of the same side as the primary wires of the transformers which is sandwiched between the transformer's frame laminations and its mounting bracket? It's white on high frequency Medallions and black on the old high frequency transformers. Thanks!
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