1960 CF Martin + wanted

[capnjuan]

I'm collecting parts for a 112 style for myself but can't find .650M or .350M pots ... Does anyone have schematics for a non-trem version? Is it as simple as removing the trem-section as is?

Hi EFR and welcome to LTG; if you don't find those values, you may want to consider 500K and 250K as substitutions. The only functional difference in the values would be a few degrees of rotation on the pots. If they are any help, I have schematics for the R112 twin 6V6 w/ tremolo and the R25T twin 6L6 w/ tremolo. If you want them, PM me with your email address. In both cases, there is a DC supply to the oscillator tube (12AX7 both models) and a return leg that connects with the signal line. If the oscillator wasn't there, the line section wouldn't know the difference and you'd save a tube, a socket, and some energy in the power supply. Most oscillators including these Martin / Dearmond designs oscillate whether the trem function is engaged or not. When switched off, the circuit's output is just grounded - the tube isn't switched off. Does the 110 rely on PECs/packaged electrical circuits? If so, how are you going to get around them?

Good luck with your project! CJ

 

[EFR]

Hi CJ-

I'm just building straight from the schematic, the 110 doesn't show PECs like the 112 with PP 6v6. I'm using a 1M and 500K for the 110, I'll probably end up using what you suggested for the 112, I was just curious to see if there was any problems going that route.

I'm omiting the tremelo on the 110, it's going to be a very simple amp with power switch on the volume control, and using 6aq5 in place of 6v6 with a pentode/triode switch for power reduction with 2x8" speakers, it's for my nephew who lives with my in-law's and I would like to remain in everyones good graces by making him a sweet sounding bedroom amp.

Check your mail, I'm interested in those schematics, I also am building a 5e7 for myself, but if the RT25 is to the 5e7 what the RT15 is to the 5e3, I'd rather do that!

Thanks, Erik

 

[capnjuan]

Hi Eric, schematics on their way. The R25T is something like a Pirate's treasure map; probably a good result except some of it is missing; the upper left corner / input jacks but it does have an interesting work-around for fixed-biasing without a separate transformer bias tap. By contrast, the 112 is complete and probably can be used to cover what's missing in the R25T and yes, peace in the family is a good thing. :wink: Good luck with your project! CJ

 

[EFR]

Finished the RT5 based amplifier for my nephew, this thing sounds great!

I changed a few things to try and make it quieter and compress a little more and was only partialy succesfull, tone and squash is really nice but this thing is amazingly loud for ~6watts! I replaced the 500 ohm resistor at the input of the power supply with a 10H choke with a DCR of 446 ohms, and used a 6AQ5 (6005) instead of 6V6. I was worried that the 6AQ5 would meltdown at 350+ volts on the plate but it's doing fine. I used a 16 ohm output tranny that I had so I used 2X 8" old alnico speakers that are part of why this thing is so loud. I also eliminated the tremelo circuit. I didn't add a triode switch because I was afraid my nephew might accidently switch it with the amp on, but I bet it would be really nice addition sound wise and I may test it out before I send it off to him.

It begs to be played wide open, and works great for slide with a thick power tube distortion and plenty of compression with the 6x4, choke, and 7-pin single ended power tube squashing things down, I know why kimock likes to use these things for slide.

Thank you Mojohand for sharing the RT5 Schematic.

Can't wait to get started on the 112 for myself, and I may have to build one of these for myself as well, it would make a great recording amp.

Erik

 

[capnjuan]

Hi Eric; congratulations on your new build! If you get a chance, post a pic or two including chassis shots. CJ

 

[Default]

yup, definitely want to see some shots!

 

[EFR]

Put some pics over on Flickr;
http://www.flickr.com/photos/35538821@N04/3290970213/
http://www.flickr.com/photos/35538821@N04/3290969139/
http://www.flickr.com/photos/35538821@N04/3291787144/
http://www.flickr.com/photos/35538821@N04/3291787388/

Kind of embarassing, but remember this is a junk box special built on an old baldwin/leslie chassis, lots of scrounged parts, less than $50 into it. Wish I could post a sound clip, then you wouldn't care what it looked like. May look nicer when it's hidden inside a combo cabinet.

Enjoy,

Erik

 

[Default]

"A loving personality will make a plain girl beautiful to all."

Translated

"Dang, but that thing sounds good!"

Keep your eye on Daddy's Junky Music on Ebay. Every once in a while, they'll get in a dead Behringer - they blow mainboards like popcorn. Decent cabs, comes with a 10 inch Jensen and the chassis is big enough to drop a tweed Deluxe board in. I've one that's getting converted into a 6bm8 amp in the very near future.

 

[capnjuan]

Hi Erik; looks great! As they say in golf, there are no pictures on the scorecard. Congratulations! CJ

 

[EFR]

I spoke with my old retired cabinet builder friend last night (he worked building cabinets for JBL and Altec in the early 70's and has a nice shop with dove tail jigs, clamps, etc.). I've already got a handful of old jensens from the leslie cabinet and my organs, and plenty of 1/2 ply on hand, and a roll of blonde tolex that I saved from the dumpster, my brother in law runs his families painting bussiness and I guess they used it as a wall covering back when that was the groovy thing to do.

I just need to get ahold of some knotless pine boardand then head over to his place to make cabinets for the three amps I'm working on! Picking through some 10" x 3/4" pine shelving from Home Depot should do the trick.

Don't worry I put an old EV in the leslie and run it off the organ's amp. So the Jensen's are not being used (yet) and the organ is still functioning.

Should be fun!

-Erik

 

[capnjuan]

Hi Erik; you sound like you are well on your way. If the purpose of the plywood is a speaker baffle and it isn't cabinet-grade, you might want to consider some 9-ply Baltic birch like this on eBay. Stronger than builder-grade material and considerably less likely to delaminate and buzzzzzzzz .... If you don't want to bother and you use some garage stock, after you cut the speaker hole, at least consider drizzling some Elmer's or equivalent into the face of the new cut to bond the edges of the laminations together. Doing so will offer some protection against a serious annoyance downstream. CJ

 

[jp]

Here we go again!

VINTAGE 1960 DEARMOND R5T

 

[capnjuan]

Thanks JP: interesting comparision between the OT in the auction amp to the OT on the TQ / Clarksdale linked here I guess I was expecting a beefier piece of iron on these ... also not seeing those PECs like other Martin/DeA amp versions.

 

[Default]

Since when do you need a shield on a rectifier tube?

Also looks like only two original caps left. Must have been owned by a player, not a collector. :lol:

 

[capnjuan]

That Jensen 10S has a small, shallow magnet that wouldn't interfere with the tubes. Considering the higher cost Qs and Rs, I wonder if it was chosen for its fit as opposed to its tone ... ? I like the racked caps; a certain wannabe ampista in FL does that with retro work.

 

[capnjuan]

Martin/DeArmond R5 on eBay Same tube lineup as a Silvertone 1471/1481 but with a slightly larger output transformer ... good condition.

 

[jp]

Spotted that one too capn. Wonder how high this one will go?

 

[capnjuan]

Hi JP; link to the seller's photobucket pics Here. If it goes for big money, it would just about have to be a collector looking to fill/upgrade a gap in his DeA/Martin lineup and not tone implications. Cathode-biased gain stage and a cathode-bypassed 6V6 ... not exactly a design break-through and the transformer is smaller than Jeff's Weber W022905 on his 1471 ... but ... never say never ... :shock: John

 

[capnjuan]

$806.XX .... too much label, not enough amp?

 

[jp]

Maybe an MM tranny upgrade will get it to sound like its big brother? Hmm. . . for $806.00 I could get a nice SF Princeton Reverb, or for twice that much I could ring up Ole Zeke.