1960 CF Martin + wanted

Default

Super Moderator
Platinum Supporting
Joined
Jul 30, 2007
Messages
13,596
Reaction score
3,008
Location
Philly, or thereabouts
Guild Total
11
jnick1947 said:
Thanks for that.
However, it does this by reducing the voltages on the output and driver sections simultaneously with voltage regulators. Stay tuned.

Definitely! Is this using fixed or cathode bias? That's the part I'm curious about.
 

dklsplace

Senior Member
Joined
Apr 29, 2001
Messages
3,325
Reaction score
0
jnick1947 said:
I have begun building a version of the 112 that will have switchable 12AY7 and 5879 pre amps with switchable supply voltages (suitable for harp, or, guitar) and Power Scaling for the output section. Power Scaling (developed by Kevin O'connor of London Power) does what attenuators are supposed to do - allows the amp to be "cranked" at ANY volume. However, it does this by reducing the voltages on the output and driver sections simultaneously with voltage regulators. Stay tuned.

I want one in a 1x15 please! 8)
 
Joined
Jan 15, 2008
Messages
4
Reaction score
0
Power Scaling will handle either type of biasing. Cathode biasing is easier, as one does not need a tracking bias supply. Kevin has produced a more or less encyclopedic series of books (The Ultimate Tone 1-5, and several others) that detail just about everything one can think of having to do with MI amps. The last one published (#4) - which came after #5 - goes into power scaling and super scaling - where one uses a small amp to drive a booster amp that actually reflects the speaker load back to the driving amp. The books are not inexpensive, but are beyond anything else out there, IMO.
Check out the londonpower.com web site.
You lucked out: I am building the amp in an old 2-12" Cordovox amp case that has a new baffle for a 15" EM1500 (the last of the real Jensens - with a nice, mushy, seamed cone) that I rescued from a Leslie.
 

Brown-Recluse

Junior Member
Joined
Jul 13, 2008
Messages
90
Reaction score
6
I started collecting/accumulating DeArmond and Martin amps about 15 years ago. That was before the prices got so high. It all started with the little single ended versions, the R10 and R10T, which are little screamers. The single 12" models with 2 6V6 power tubes are very cool too, followed by the 2 6L6 R25T amps. I currently have 5 Martins, 3 with tremelo and 2 without. I had a 6th Martin that I purchased off of ebay several years ago. I sold it to a friend and eventually bought it back. Sometime later I sold it to another friend of mine with the understanding that he had to give me first crack at buying it back.

I also have about a half dozen of the baby DeArmonds. The Martin 110 amp that recently sold on ebay was the only one of those that I have ever seen or heard of. The other recent ebay auction for the R25 amp with the single 12" speaker was only the 3rd one of those that I've heard of or seen. I have 3 of the R25T amps with the standard 2 10" speaker configuration. I also have about a half dozen of the 2 6V6 amps.

I havent' gone through all of the amps to catalog the little details, however, I did pick through 4 of the Martins a few weeks ago to check out the transfomer information.

Here is the model, serial number and transformer information I collected off of those 4 amps:

Model: 112T
Serial No. MC2-1301
Power Transformer: PT-5201 549-6045
Output Transformer: T-703 549-6050

Model: 112T
Serial No. MG2-1341
Power Transformer: PT-5201 549-6045
Output Transformer: T-703 549-6050

Model: 112
Serial No. MA 0320
Power Transformer: PT-5201 549942
Output Transformer: T-703 549941

Model: 112
Serial No. MM9217
Power Transformer: PT-5201 549942
Output Transformer: T-703 549941

There are definite variations in the way the amps' model designations and serial numbers were noted on the tube charts. The transformers, power and output, for all 4 amps were made by the Midwest Coil & Transformer Company. Both non-tremelo amps have the same transfomer codes from late 1959 while both tremelo amps have identical tansformer codes from late 1960.

I've seen quite a few people reference the internet article that claims the amps were made by the Allen Organ Company. I never really thought that was true, however, I have no way to prove that. As time goes by I will try and collect and post more details on my other amps and possibly get some pics posted too.
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
Hi Brown Recluse*: Here's another Dearmond R15T: eBay Listing Not much technical detail, killer cosmetics in the auction pics. $1,575 min plus undisclosed reserve:

dearmond112.jpg



*Poisonous spider Wiki Interesting choice of screen name ...
 

dklsplace

Senior Member
Joined
Apr 29, 2001
Messages
3,325
Reaction score
0
capnjuan said:
Hi Brown Recluse*: Here's another Dearmond R15T: eBay Listing Not much technical detail, killer cosmetics in the auction pics. $1,575 min plus undisclosed reserve:

Sweet! However the "had my guy do the minimum necessary" gets me.......I mean, an amp pushing 50 years old....if the caps haven't gone bad, they will. Just do the job, quit dinkin' around & get it right the first time! :?
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
dklsplace said:
Sweet! However the "had my guy do the minimum necessary" gets me.......I mean, an amp pushing 50 years old....if the caps haven't gone bad, they will. Just do the job, quit dinkin' around & get it right the first time! :?
It's a beauty Donnie. On the question of how much to do / not do - this is an eBay listing for an absolutely dead-mint Gibson GA8 - so fine, if I didn't own one, I'd buy this one. The pic below is from the auction;

ga8bay.jpg



I think the pic is an excellent example of doing as much as possible - what needs to be done - without needlessly disturbing original, working parts. Someone has carefully and respectfully put in the new blue inverted capacitors for the screens and preamp, the larger cylinder cap is likely a 2-section like the design calls for, and in the middle and on the far right, new 5W resistors in the power supply and cathode bias resistor. The cathode bypass capacitor has been changed but the coupling caps are original.

The 1 watt preamp cathode resistor (leftmost) has some of the jacket cracked off but I'd guess whoever did the work checked it for drift and concluded it was within spec. The missing chunk is a cosmetic thing, not an electronic one. For the continued performance and health of the amp, the maintenance has to be done. Who drives a 50 year old car with its original oil in it?
 
Joined
Aug 29, 2008
Messages
2
Reaction score
0
I acquired a Dearmond R5T amp about 7 years ago at a yard sale for $5. I was also lucky enough to acquire a schematic too. This one is basically like a tweed Princeton with tremolo. Really sweet sounding! Ill post the schematic and some pics of it tomorrow. It looks identical to the picture of the R15T posted but smaller.
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
Hi mojohand and welcome to LTG! I look forward to your pics. CJ
 
Joined
Aug 29, 2008
Messages
2
Reaction score
0
Sorry for the delay, I've been pretty busy lately. Here is the instruction sheet and the schematic for the R5T. I'll upload some pics of my amp later today or tomorrow.



 
Joined
Aug 26, 2008
Messages
4
Reaction score
0
Wow! I've been looking for that schematic for a long time! Thanks Mojohand!

I have a Martin 110 that I absolutely love (just like the DeArmond R5T, except without tremolo).
Here's a pic:

Picture043.jpg
 

capnjuan

Gone But Not Forgotten
Gone But Not Forgotten
Joined
Nov 29, 2006
Messages
12,952
Reaction score
4
Location
FL
Sweet biyf and welcome! Got any chassis shots of that amp? Same thing?; single-ended 6V6? CJ
 

Brown-Recluse

Junior Member
Joined
Jul 13, 2008
Messages
90
Reaction score
6
capnjuan said:
jp said:
$1,426.00 ... :shock: I wonder if this is a case of people just backing off because they thought it would be in the $2,500-$3,000 range ... ?

That might be part of it. The state of the economy probably plays a big part. Also, more of these started to show up for sale once the prices got so high . Although they are fairly rare, they are out there.
 
Top