Thrift find - m' first dynaco - vintage original circuit-SP-7- stereo 70 dynakit

Hi Everyone!

I have just found this on the floor of our local charity shoppe. Just an amazing find. I previously have owned a few different Tube Hi-Fi amps, one I still have in my possession is the fabulous HH Scott 222c .




here is link to the youtube video slideshow I made of the Amp :


https://www.youtube.com/watch?v=th9JsYJSglw



This Dynakit may just trump that HH Scott - amp. At least without mods. The Scott I have does have some noise and needs a bit of work. This is all coincidental and not a serious evaluation.
I have not modded either and they are both stock the way I found them.

The Dynakit looks like it was factory wired, but I Can't be sure at this point.

The previous owner chucked it out as they could not figure out why the right channel is gone. I'm almost certain it's just the circuit board on the top, and just a bad cap or resistor. I'm just going to order an upgraded circuit online (there are a few choices for under $60.00) I am gravitating towards the circuit that just upgrades so I can use more common tubes -7199's are very rare now-, but still close to the stock design. Oh, the only tube missing was the rectifier 5AR4-GZ34 and as luck would have it I had one of these in my collection ( i forget what I pulled it from) and it's a seam top Japan Mullard spec'd tasty treat.

I had to reconnect a few wires under the chassis to get this running. The previous owner had tagged the wires , and looking at the guide, it was proper so I retagged them with clearer writing for kicks. (it was on decaying gooey masking tape) Took me an hour to resolder a few points, install a new power switch I took out of a very nice Lambda power supply that i extract parts from and fired it up. There was noise and hum.
When I hooked up the RCA jack on the front, that eliminated it and is super clear. There is a Very-Very low level 60-80 cycle hum present, but I have heard that in even mod'd tube amps, it seems to be something hard to get away from.

I first tested on a crappy Sony ghetto blaster speaker so I wouldn't damage anything important..after that passed fine, I hooked up the JBL Century 100.
I can only use MONO right now due to the bad circuit in the right channel..but no worries here. I listen to alot of Mono Lp's and such so It's not a worry. Just to have this running in tandem as a filler for super tight and clean powerful bass, with my Yamaha A-760 amp, is sweet as anything I have heard. So next step is to order a new board for it, and then decide what to do next. I'm not planning on modding this thing like crazy, just slightly to get it to spec and enjoy it, because if I want to mod it I will just emulate it on a different chassis. I want to keep this thing as original as possible. One thing that was weird, when I was installing the EL34's I noticed the bottom middle posts broken off 2 of the 4. I thought the tip was busted too, but thankfully they are not..the vacuum is still sealed. I did not see the pieces floating around inside. Was this done by the previous owner? if so, why? I use one on each side to be safe. one of the 7199s has DYNAKIT printed right on it! The other has Sylvania in yellow, yet they look identical grid plates, ect. Interesting! Black cat's in there original(like i said, nothing has been modded)
I absolutely feel very lucky to find this, and a great compliment to my record collection. The video shows some streaming Reggae from itunes, and then some bits from the Canadian Mono 1st Pressing of Beach Boys Pet Sounds and the band called the ID with Jerry Cole. Sorry about the short segments, my camera only takes 15 second video shots. (totally rediculous) Now I just have to find some replacement nuts and bolts as the previous owner just simply forgot or never decided to reassemble this beauty. I'm sure that's why it ended up in the Charity shoppe for a cool $15.00 - A bit about that.. I Had been in the store earlier that day, and I found a Hallicrafters Shortwave radio which I wanted very badly. IT was $15.00 too. So I went to the bank and came back. while I was loading it, out of the corner of my eye, I saw the familiar black grille of a tube amp on the floor. Someone else had TESTED This and left it!! Boy am I lucky. ANd whoever was testing it, are lucky they did not get a Shock as there were exposed wires. ANd this past week has been a lucky week for great equipment for low prices. I also got a Heathkit AUdio Scope aD 1013 a few days ago. A great compliment for the hi-fi head I am. YOu can see it briefly in the video. The preamp is a Mackie Mixer U.420d.

Tonite I went over the right channel underneath the hood with a fine tooth comb (so to speak)
and I came up with the fix!!! I got the problem solved and nothing is leaking, blown, smoking or feeding back.

The problem was the power mains that is hooked in tandem with the front Pre amp jack, one of the cables
was totally just unhooked and this was the essential wire that drives the right channel to power as I see now.

I now have a fully functional stock Stereo Amp! I'm in heaven! For real!! what a compliment to my vinyl collection.
And as many know it sounds so good. It's freaking loud too! I was testing it and my girlfriends daughter was entranced but not used to those DB's! I was just gobsmacked by how clean the sound is. what a pinnacle of consumer hardware. It is driving the 8ohm JBL century 100's with no problem. Playing reggae shakes the house with ease. I can't wait till tomorrow daytime to test running dual mono to see what can be acheived.

An old-timer Tube hi fi head who lives in Vancouver passed on a cheap and ultra effective tube-cooler
DIY that his A/V club in the 60's - 70's came up with. It's with a simple metal clothes hanger
and you coil them and they drop the temp -several- degrees at least. I'll take pictures and post them soon. I made one for each tube last night, it took about an hour to do all of them. I can post how to do it step by step also. the bonus is when applying them, it also is extra protection of your tubes. You can also run them to the cage and the cage acts as an extra heat sink, but for a stock Stereo 70, that's rather overkill, because the tubes run cooler than most amps to begin with. Even the 1959 review makes that very clear. They look pretty darn cool, kind of like a tesla-lab- look You can paint them with high heat paint too for ultra style. I have them bare for now. ANd if you have extra shop equipment you can do other funky stuff. peace

GREAT FIND!

As for the tubes with the broken center posts: That probably happened by accident to a former owner.

Some people wiggle the tubes too much when removing them and break off the middle posts in the process. As long as
you can tell where the keyway was, you can carefully put the tubes back. I have lots of old tubes that are like that, but that still work
and are too good to throw out.

GP49 wrote:GREAT FIND!

As for the tubes with the broken center posts: That probably happened by accident to a former owner.

Some people wiggle the tubes too much when removing them and break off the middle posts in the process. As long as
you can tell where the keyway was, you can carefully put the tubes back. I have lots of old tubes that are like that, but that still work
and are too good to throw out.

righteous..that makes perfect sense. And I'm very happy they still work. A nice matching set of 4 tubes. Thanks for your reply.

oatstao wrote:

GP49 wrote:GREAT FIND!

As for the tubes with the broken center posts: That probably happened by accident to a former owner.

Some people wiggle the tubes too much when removing them and break off the middle posts in the process. As long as
you can tell where the keyway was, you can carefully put the tubes back. I have lots of old tubes that are like that, but that still work
and are too good to throw out.

righteous..that makes perfect sense. And I'm very happy they still work. A nice matching set of 4 tubes. Thanks for your reply.

Hint: if you would like to replace the center post, check out Antique Electronic Supply (http://www.tubesandmore.com/). They have a replacement keyway (part# P-STKY-1) that just slides up over the tube pins.

Best Regards,
Charlie

Thanks y'all. Very good tips and thanks so much for the link. the tubes measure like new so I may just order those. They are a matched set of 4..wouldn't want something silly to happen!

I added new speaker binding posts I sources from wrecked teledyne speakers from 1980 and very unique plastic.

The amp sounds like new. Seriously. I'm very surprised as I have to replace those old caps on the top and the selenium rectifier and the bias caps.. then I'll breath a bit easier. Major tube fails can happen if that selenium goes.. I don't think I have to spend more than $10 bucks!

Fantastic find. TubeNoob will laugh at me for saying this, but I keep on dreaming about finding a Linn LP12 with all the stinkingly-expensive updates at a thrift store for $10... I have been looking for years now ;-)

I have only on one occasion found a piece of tube equipment at a thrift store, sadly it was in such a bad state that I gave it a "pass it by and don't look over your shoulder" treatment. It was a Chinese or Korean brand I have never heard of before in my life - not Dynaco, McIntosh or anything like that.

-- JunkyJan