Dunlap Clarke Dreadnaught 1000 amp

[Richard Swann]

Hi,

I have a dunlap clarke dreadnaught 1000 power amp that i picked up second hand. It sounds great & i have been told its a good piece of kit... it certainly built like it is !

I cant seem to find much info on the net about them & i was wondering weather anyone knows of the spec of this amp such as watts rms per channel into 8,4 & 2 ohms ( presuming its stable @ 2 ohms ).

Any other info would be usefull as i'd like to know a bit more about the amp.


Thanks in advance

 

[djk]

I think it was 500W/8R per channel.

Each channel was a bridged output stage if I remember correctly, about ±60V, 2N6031/2N5631 outputs.

Drives 4R OK, 2R is a death wish.

http://home.rochester.rr.com/bkdavis/dunlapclarke.jpg

 

[Mark A. Gulbrandsen]

Originally I think it was three partners... Dunlap, Clarke, and McMurrow as some of the amps had the initials DCM on them. They made about a half dozen models. I remember those guys very well at the Hi-Fi shows back in the mid 70's. They were real nice guys too, I wonder what ever happened to them. The stuff was built like a tank, especially considering the state of semiconductor technology back then, which compared to today was pretty crude. I always wanted to latch onto any one of them just as a piece of memorabilia. If anyone runs into one thats available please let me know...... BTW: that was the same time period as the BGW "Arc Welders Special".

Mark

 

[JJT]

My schematic of the front end shows 2n5550/2n5560 input trans,
inline voltage reg between both halfs of the driver. The driver
is on plug in boards, like PC cards. IF I remember right,
and the pix helped, it was 500wrms into 8 ohms. Ruggerd,
LOUD stuff, sold local here by a HiFi store (still on rt9),
I forget the name, but back then it was the BIG fancy
HiFi store..oh yes, 'Natural Sound' is the name.

http://www.natural-sound.com/

I called them, and they remember it, but long ago.

My schematic shows 1974.

They are big blueprint sheets, or' Id post them,
maybe I can shrink the driver stage down.


JJT

 

[poobah]

I still have a BGW... still cranks too!

 

[Nelson Pass]

Dunlap stands as the best high power solid state designer of
that era. An extremely nice guy as well.

 

[latala]

I seem to remember that John Farlow who went on later to design and market Exposure amplifiers @ hove near Brighton had something to do with these
Iam not totally sure as I have not seen John for about 20 years
As I remeber he was a nice Guy who would help if he could
Also he used to ride a Ducatie and as a biker he can not be all bad Regards Trev

 

[Mark A. Gulbrandsen]

Would love to see the schametics if at all possible...

Thanks!

Mark

 

[Don Nebel]

Hello, I just bought a Dunlap Clarke Dreadnaught 1000 amplifier on ebay. I paid $100. I went to the local library and found in the 1979 Audio magazine annual buyers guide that the amp was rated 250 watts per channel into 8 ohms and 800 watts per channel at 2 ohms. The amplifier had a retail price of $1,500.00 and was made in Waltham, Ma. USA. It weights 75 pounds. The amplifier has (4) 2N6609 and (4) 2N3773 output transistors per channel and a 114vct. 15 amp transformer.I bought the amplifier Knowing that it needs repair and I have not attemped to plug it in. There are not any burned traces or components visible in the amplifier but, there are some unattached wires. I would like to locate a owners and a service manual for this amplifier.What should I check before I plug this thing in and turn it on? I understand that this amplifier is a rare item and I don't want to cause any damage that can't be repaired.

 

[Nelson Pass]

If you can't get an owner's manual, you can try tracing the
circuits of what you've got. I know a little bit about it, but an
actual schematic would be helpful and interesting to everybody.

I don't doubt that with some help you can get this restored,
and as a classic piece, I think it's worth the effort.

 

[kASD]

Check this out...I think that guy could help you...

http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1029813898&openflup&3&4#3

 

[destroyer X]

Schematic will be very interesting.

regards,

Carlos

 

[gearheaddruid]

The bench pic

Destroyer, that looks like my audio torture bench in the backround of the amp picture!

 

[destroyer X]

Mine too.

regards,

Carlos

 

[Mark A. Gulbrandsen]

Don,

If you ever decide to sell it please give me first dibs on it!!!!!

Thanks,
Mark

 

[Don Nebel]

Hello. The Dunlap-Clarke amp that I am working on has been worked on by the previous owner. One circuit board has the original semi's in it, the other board has NTE replacement parts. I am having a hard time finding information on some Fairchild semi's that were replaced with the NTE parts. The Fairchild part is:S42728. I need to find a suitable replacement for this part. Thanks, Don Nebel

 

[Don Nebel]

Hello, I did some searching to try to find information on Dunlap-Clarke amplifiers. I did manage to reach Mr. Dunlap through a friend of his. As Nelson Pass has stated Mr. Dunlap has moved on to another interest. Given Mr. Dunlap's responce to the inquiry about his amplifiers, I think that the door for future inquiries is closed. Don Nebel





\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\


Don,

I apologize for not getting back to you immediately. I was waiting on Ron's response to your inquiry. He is a Cardiologist and often is extremely busy. Below is his response. I hope this is helpful.

Alvin Foster
Boston Audio Society
--------------------------------------------------------------------------------------------------------------------------------
Alvin I sent an e mail on Dunlap Clarke 2 days ago while at work.

I will re-iterate. I responded to friends and people I know well who own Dunlap Clarke for at
least 10 years beyond the demise of the company.

Repair of the amp is straight forward. The output devices are 2N5631 NPN and 2N6031
manufactured by Motorola and Fairchild semiconductor. Both companies had trouble
supplying devices with high enough breakdown voltages. Therefore, we selected them
by hand using a Tektronics curve tracer. We looked for 180V breakdown voltages.
I am sure there are better complimentary output devices available today.

One can measure from the output devices to the hot speaker terminal with the driver circuit
or driver boards removed with an ohmeter. If it measures a short circuit a short is present in the devices in that half of the outuput circuit (They are in parallel and can be removed one at a time until the short goes away.). Measure from can of both positive and negative devices. The device cans are basically at
the positive and negative power supplies. Replace all shorted devices and retest. Shorts should be gone.
No current should be drawn when power is supplied to the unit with the driver boards out of the printed
circuit connectors.

Replace the main power supply fuse with a low current 500 MA fuse.

All driver transistors on the circuit board can be removed and tested. The input transitors
2N 5551 rarely fail. Pre-drivers should be removed and tested. the only difficulty one might have
without a schematic is if a resistor is burned or shorted. The amp will bias up with as little
as 25 volts AC supplied from a Variac with the repaired board in place. I usually use an HP with a voltmeter and a current meter on the front panel. The one you have was custom built by me for testing amps.
There are two adjustable resistors or potentiometers on the board. One adjust the DC offset
at the output terminals and the other adjust the bias current for the output stages.

The technical manuals and circuit layout are God knows where at the point. Ira sent
me some data he acquired some time ago but I have no idea where it is. At this
point I am not prepared to serve as a repair service for Dunlap Clarke given almost thrity
years since the company was in business. Ron

 

[mmorris]

Dunlap-Clarke Dreadnaught 1000

I have a Dreadnaught 1000 which I am currently listening to driving Dalquist DQ-10s.

I was told when I acquired it about four years ago (I traded it for an old Electrohome preamp!) that it was a prototype - about which I am somewhat sceptical, although there are a couple of cosmetic items that do seem unfinished, and the only serial number is scratched on and appears to be 007 - so maybe the information was correct.

It came with a photocopied schematic and, if I remember correctly, a photocopied manual, which I have stored in my basement. If anyone would like copies of these, e-mail me and I will hunt them out.

It is an extremely good amplifier, if not as airy as the Sonic Frontiers tube amp I use in my main system. A couple of years ago I lugged it around (quite an achievement, as anyone will know who has picked one up) to a couple of dealers to compare with more modern solid state amps, and not until the comparison amplifiers got into very serious bucks did its limitations start to show - and then mainly in the depth of the soundstage.

Thank you Don Noble for getting that information you posted.

 

[sepeskoe]

Dunlap Clarke equipment

I am a former Dunlap Clarke employee (I worked there part-time and summers from 1975-1977). I spent many hours sitting at that Tektronix station in our Waltham factory, selecting components one by one by hand. Despite that singularly boring job, I concur with earlier posts: Ron Dunlap is one of the nicest gentlemen you could ever hope to meet. Mel Clarke was a pretty good guy, too. (Seeing Ron's note, as forwarded by Al Foster, reminds me of our standard assembly and test procedures, etc. Other postings remind me that the Dreadnaughts were designed to drive demanding dynamic loads like the new electrostatics and big panels: Dayton-Wright 3s, Magneplanars, KLH 9s, DQ-10s, etc., where impedance could drop below 1 ohm, but the Dreadnaughts would continue to put out full clean unclipped power. Those were exciting times in high-end audio.)

I got almost 30 years of service out of my two Dreadnaught 1000's. I'm sure the internal electronics are still fine, but one or more of my output devices has blown. I got lazy and purchased new amps rather than repairing these amps. However, Ron's note reminds me how simple the troubleshooting would be; I'm going to find a bench and open these guys up. One of the amps is a prototype (I think it's serial # 1 from 1972 or 73, I believe). Other than the face plate, it does not really resemble the production units except in terms of performance. The other is a 1976 or 77 production unit.

We also built pre-amps. I am still using my 1976 Model TEN FET stereo pre-amp. (I have a perfectly good prototype pre-amp, too, but sitting unused on the shelf.) Dunlap designed some rock solid equipment - the sobriquet "Dreadnaught" was indeed well earned.

I'm glad correspondents like the amps -- we were proud to build them.

 

[Nelson Pass]

I still think it would be a service to the audio community if
someone were to trace the circuit out.