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Help with a new 45 SET amp....

analog addict

analog addict

Glory or Death!
Subscriber
Well, I fell into a beautiful DIY 45 SET amp courtesy of Barrynsue. I want to thank him and Homer for making this acquisition possible.

Pix first....

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Now for the admission of truth....:sigh:

I am keen to fire this bad boy up, but I don't know how long Barry has had it stored, so I am tempted to bake it, and will definitely variac it up. It didn't come with a schematic or manual, just the amp itself. So, I have a lot of questions.

1) I don't see an index pin or any marking on the underside of these 45 tubes. Howinthehell do you figger out which way to put them into the sockets?

2) Is it OK to variac them up like a PP amp? What tube(s) should I put in it before applying power? The rectifier for sure, but what else? Run it up to 90 VAC and then put the driver/power tubes in? Put the driver tube in earlier?

3) Hadn't heard of a 5692 tube before, but I guess it is a premium 6SN7. Red based RCA. Interchangeable with a 6SN7? Also has a 5V4 rectifier "Made in England", guess it's a Mullard. And the RCA 45's look identical, with a 035 date code. Can I safely assume this is a very nice set of tubes?

4) Can anyone tell anything about the circuit from the underside view? Looks like there are 2 chokes mounted underneath. Do all the caps look like new/non-leaky type manufacture? What can I assume about the other side of the PCB? Leave it alone until proven otherwise, or should I take it apart and check it out?

5) Anyone recognize the iron? Good stuff?

6) Do the 45's need to be matched? I have an extra pair a friend gave me earlier this week, but haven't even run them through my tester yet. However, they are different brands....:scratch2: How might I set the bias?

7) Anything else I'm forgetting? Anything I should make sure and do?...:scratch2:


TIA, as always......:thmbsp:
 

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Damn, that's purty!! Now why didn't I ask about that amp? I saw the pic and thought about it...

I could be picking the wrong number off the transformers, but 138 is the EIA code for Stancor. Quite possibly very nice iron! :yes:

Don't do anything rash, like blow that sucker up... or any of the tubes, for that matter!
 
Thanks guys

markgod said:
look at the pins on the 45 tube ,you have 2 different sets . Match them to the tube socket .
Click to expand...

I don't quite understand....:scratch2:

I'm not taking for granted that they are in there the right way to start....:no:

The pins don't seem to have any markings. Is there any way to use an ohm meter to determine what's what???

EDIT: OK a little research and it seems that 1 and 4 are the filament, 2 is the plate, and 3 is the grid. Guess that's a start...
 
Allan,

It has been stored for at least THREE years although I had run it on my variac about a year ago. Never hooked the sucker up though to see how it sounded and only powered it up to see if it was in fact "working".

That's all I know about it and hope it sounds good. There are some decent quality components and all should be good but that's the extent of my knowledge.

Barry
 
Alright....Tell me if I'm wrong

A 45 uses 2.5 VAC or VDC at the filament, 50VDC grid voltage and 250VDC plate voltage. Max power output is expected to be 3-3.5 Watts.

Plenty for Model 19's or K-horns....:thmbsp:
 
barrynsue said:
Allan,

It has been stored for at least THREE years although I had run it on my variac about a year ago. Never hooked the sucker up though to see how it sounded and only powered it up to see if it was in fact "working".

That's all I know about it and hope it sounds good. There are some decent quality components and all should be good but that's the extent of my knowledge.

Barry
Click to expand...

Thanks Barry. I'm just trying to be careful with what appears to be a high quality piece of gear. Learning as I go too....:thmbsp:
 
Ah...I see....

sloober said:
Don't the pins have different spacing so they only go in 1 way? Nice score dude! John
Click to expand...

The TDSL page shows 2 different sizes to the pins, and upon closer examination, 2 are thinner, and two are thicker...Duh!...:stupid:

They can actually only go in one way....:thmbsp:
 
In all likelihood, three of the pins are the same size, and the fourth is slightly larger. The larger pin will go in the larger hole. :thmbsp:

Well, maybe not.. that's with the 2a3 SET amps I have. The 45 amp is too far in the back to look. :sigh:
 
analog addict said:
A 45 uses 2.5 VAC or VDC at the filament, 50VDC grid voltage and 250VDC plate voltage. Max power output is expected to be 3-3.5 Watts.

Plenty for Model 19's or K-horns....:thmbsp:
Click to expand...

Right except that the 45 makes a little over 1.5 watts with those values. If you up the plate voltage to 275v and a grid voltage at -56v, it will produce 2 watts.
 
2 large and 2 smaller pins, same as the 2A3 and 300B.

You will only get about 1.5 to 2w out of a 45 SET but they are the best watts I've ever heard - should work great with K-horns or maybe 19's in the right room.

The 5692 is similar to the 6SN7 and can be substituted in most circuits from what I understand. I really liked a 5692 tube in the 6SN7>300B amp I had. The Red based RCA in your amp is very good and widely regarded as one of the best 5692's available. Actually, all the tubes in your amp are first rate.

Should be interesting hearing how this works out; I suspect you are in for a real treat hearing this on the right speakers.

Nice buy!
 
Last edited:
AA,

If you ever decide to sell it, I only ask that you give me the first opportunity to buy it back!

Hope you enjoy but knowing you, it won't be long before a change is in the air.

B
 
No worries!

barrynsue said:
AA,

If you ever decide to sell it, I only ask that you give me the first opportunity to buy it back!

Hope you enjoy but knowing you, it won't be long before a change is in the air.

B
Click to expand...

...but I hope you won't hold your breath....:D Been looking for a nice SET amp for quite awhile.....:yes:

On another note, how important is it that the output tubes be matched? The two RCA's have a mutual conductance of 1400/1850 and 1800/1850. I have the other two spare 45's, one of which is right around 1400/1800 also. That one is a "Champion" branded tube...:scratch2:

Also, what would be the life expectancy of a 1400/1850 tube? Do these tend to last a good long time, or do they burn up fairly quickly?

On another note, I found a spare coke bottle RCA 5V4G that tested nice and strong on the ol Hickok 533A. Would there be a sonic preference between it and the Mullard, which tested even a little stronger?
 
Hello!

I am assuming that if you own a variac you also know to have a dummy speaker load hooked up before powering that baby up. Enjoy! Robert
 
analog addict said:
Well, I fell into a beautiful DIY 45 SET amp courtesy of Barrynsue. I want to thank him and Homer for making this acquisition possible.
Click to expand...

Nicely executed amp. I like the turret board underneath...has a military or high reliability industrial look to it.


3) Hadn't heard of a 5692 tube before, but I guess it is a premium 6SN7. Red based RCA. Interchangeable with a 6SN7? Also has a 5V4 rectifier "Made in England", guess it's a Mullard. And the RCA 45's look identical, with a 035 date code. Can I safely assume this is a very nice set of tubes?
Click to expand...

Tubes look great except for that 5V4. To the best of my knowledge, a true 5V4 was never made in England or Gt Britain for that matter. Closest they came was the GZ32 which is quite nice. Your 5V4 appears to be Russian in origin and is more similar to a 5Z4 than a 5V4. The clues to this from your pic are 1. The mica side spacers at the top are typical of Russian construction. 2. The tube is labeled "5V4G" which implies an "ST" bottle like the 45s but this is a straight sided "GT" envelope. Something must have been lost in translation. 3. During the late 60s and thru the 70s and 80s a lot of Russian tubes were imported to the US with "Made in England" on them when the true english tubes typically were made in "Gt Britain". Another clue would be the presence of a "flying saucer" getter holder...can't see it in the pic...but very Russian if it's there.

Although the current rectifier may be working OK, if Russian, it probably doesn't carry the ratings of a true 5V4. A real 5V4G would be a nice improvement if nothing else than aesthetic.


5) Anyone recognize the iron? Good stuff?
Click to expand...
The OPTs have a mfg code indicating Stancor but the "special" designation and the FT model #makes me think Magnequest. Regardless, they look hefty and up to the task.


6) Do the 45's need to be matched? I have an extra pair a friend gave me earlier this week, but haven't even run them through my tester yet. However, they are different brands....:scratch2: How might I set the bias?
Click to expand...

This appears to be a single-ended stereo amp so technically, there's one 45 per channel and no matching required. OTOH, it's probably feedback free too so there may be some practical advantage to matching for gain so channel imbalance is minimized. Tough to say for sure w/o schematic but matching won't hurt anything but the pocketbook.

As for bias setting, most probably this is a self bias design so nothing to set. Again, tough to tell w/o schematic or the amp under eyeballs.

Bottom line: Enjoy!
 
Hi guys,

Nice amp! Looks very much like a JE Labs "Simple 45" but using a 6SN7 instead of the 6SL7. I have built a few 45 amps and a few 2A3's too. There's just something about that DHT sound! I am also a fan of the 5V4. They are cheap enough and seem to last a long time if they are not stressed...plus I love the look of the ST types! This has making me thinkin' about those Electra-Print outputs I have on the shelf...:scratch2:

Happy listening:music:
Tom
 
OK, just a few guesses about this amp. The PS choke looks to be mounted on the back, with the single filament transformer for both 45s on the side. The coupling caps, the long, lighter colored ones look like vintage Paper in Oil types. No telling how old they really are, but if you see any signs of problems, I would replace them right away. The large dark colored caps look to be labeled Nichicon. They look like rolled paper jackets and I have never run across Nichicons in that style. They might be decoupling caps for each 45 tube? That first blue cap looks similar to an Atom, but it's not as fat as the ones I have on the shelf. Nice PS caps for not much $ and they are fairly reliable. I am guessing this amp is cathode biased, since I don't see evidence of a negative supply. Also, I don't think I have ever seen ratings for 45s in fixed bias mode, but I may be wrong. If you look at the brown Ohmite resistor, I would bet it's around 750 Ohms. If so, that's the common cathode resistor for both 45 tubes. It looks to be tied to the cluster of caps, with the yellow one being a small value bypass for the electrolytics. I don't see any hum balancing pot anywhere....that's somewhat strange. Maybe there are parts underneath the board that I am not seeing. If run into problems and need to replace any caps or resistors, drop me a line. I have a pretty well stocked parts bin....OK...many parts bins!:D
 
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