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Looking to get back into tubes-with 1625 output

Freo-1

Freo-1

Well-Known Member
After giving up on tube amps for some time, largely to dodgy 6550/KT88 tubes, looking to get back into the tube amp sound.

Looking for something that would provide 40 to 50 watts of power, with a degree of reliability. After talking it over with my tech buddy, came up with a recommendation to make monoblocks with 5U4 rectifiers, 12SN7 input, and 1625 (12 volt version of 807) output tubes. He has a bunch of NOS tubes of each type, they seem readily available, and reasonable cost for replacement. Was looking at cathode bias for the 1625 tubes.

Any suggestions from the group on this? The transformers and other parts are already on hand.
 
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hey-Hey!!!,
For 50W, go parallel PP, get the Hammond 1650R OPT( 5k/100W and an exceptional flyer in the Hammond line ). B+ around 350V to plates and screens and idle at 80% of plate dissipation rating.

For the front end, build what ever you'd like, but leave room to experiment widely. With that power stage and OPT you can get a truly excellent amp if you pick the front end stages well.
cheers,
Douglas
 
I too will be working on a 1625 amp. I just picked up 32 NOS ones all old Military. The only difference I see is the voltage. 6v on the 807s and 12 on the 1625s, everything else is the same. Please keep us posted as you move alone on your project.

Good luck and I will be fallowing along.

WO
 
Got a ?

My OPTs are 5000ohm but they are rated at B+ between 480-680volts

I was actually looking for more power then 50w. more like 125w. My OPTs are rated to 200w. I have most of the parts just still need a good schematic to go from. My teacher is searching his stock of 2500 to see what he may have on hand.

Any suggestions?

Thanks
WO
 
wildone said:
Got a ?

My OPTs are 5000ohm but they are rated at B+ between 480-680volts

I was actually looking for more power then 50w. more like 125w. My OPTs are rated to 200w. I have most of the parts just still need a good schematic to go from. My teacher is searching his stock of 2500 to see what he may have on hand.

Any suggestions?

Thanks
WO
Click to expand...

You'll need 790V rms across that 5k primary to deliver 125W. Multiply by root 2, and you ger around 1100V...that is the peak-to-peak voltage across the primary. Divide by two and that's 550, more or less. You'll need more than 650V of B+ to do that.

Care to look at current at full power? recall it will be AB at this point and working into 1250 Ohms. In any case that is ~340 mA rms...dig out root2 for its peak and you'll need at least two pairs and huge B+, likely better done with three pairs.
cheers,
Douglas
 
FWIW, not all 1625s are created equally, especially some of the later military ones. I've found them to be a finicky tube to work with, even on supposedly proven improved Williamson designs, but that's just me. Maybe I'll figure them out someday.
 
jaymanaa said:
FWIW, not all 1625s are created equally, especially some of the later military ones. I've found them to be a finicky tube to work with, even on supposedly proven improved Williamson designs, but that's just me. Maybe I'll figure them out someday.
Click to expand...

I'd be very interested in hearing your thoughts on the various 1625s. I have a batch of 10 NOS JAN tubes made by Hytron for a Western Electric contract approved in June 1944. I also have a mixed bag of five used and NOS RCAs - 4 JAN, one with civilian markings. Rounding out the pile is a single Sylvania made for a Tung-Sol JAN contract. I've been thinking about converting a pair of RCA MI-12188As to use 1625s instead of the much more expensive 807s.
 
My OPTs are made for Special 6550s. I will talk to the teacher and see what he has to say.

I put this one on the back burner for now as I am still building my bench and adding gear.

WO
 
If you weren't looking for so much power, that sounds like a perfect candidate for a classic Williamson amp. They were originally designed around a pair of 6SN7's and a pair of 807s. Not sure how well that design would scale to PPP though. I own an old Williamson with the ultralinear transformer and I think it sounds quite good.
 
It's not that I am after to much power? I bought these and the monster NOS UTC S-43s to be able to make a huge set of mono's. The OPT's are rated for 175/200 my teacher says no more then 125w if we want to keep the good sound.

That is for ea. OPT and I have 4

Thanks
WO
 
hey-Hey!!!,
One thing I've discovered after starting to accumulate parts for an over the top design was to start smaller. Pick a design that does not care so much about its power supply, as in Class A. Your 5k requires lower B+( or doubled current ) v. higher a-a loads. 6k6 and 6550 will let you go to ~350V of B+. Be conservative on your first attempt.

I am not going to tell you what to run, there's lots of choices...more than you've got time to build in fact. I like the less troden choices myself, and in part 'cause they're lots less money to implement.
cheers,
Douglas
 
125 watts with tubes is a lot of power and a lot of money. You get into expensive output iron, expensive and very beefy power supply design, and all of that takes a lot of space so you're looking at a large and more expensive chassis. My biggest amp is a UL Williamson with 807's. Its good for about 22 watts and it makes enough sound to shake the paint off the walls.
 
I'm looking to run a pair of 1625's per side, to get around 40 to 50 watts. I'm open to suggestions regarding the input tubes, but was thinking to use 12 volt tubes on the input as well, such as a 12SN7 or 12SL7. Can't see using 6 volt versions, just to pay a lot more for replacement tubes. Will use 5U4 rectifier.

I'll get together with my buddy to finish parts selection this week, send the chassis off to get painted, and get to work after it comes back,
 
Freo-1 said:
I'm looking to run a pair of 1625's per side, to get around 40 to 50 watts. I'm open to suggestions regarding the input tubes, but was thinking to use 12 volt tubes on the input as well, such as a 12SN7 or 12SL7. Can't see using 6 volt versions, just to pay a lot more for replacement tubes. Will use 5U4 rectifier.

I'll get together with my buddy to finish parts selection this week, send the chassis off to get painted, and get to work after it comes back,
Click to expand...

What iron are you going to use for this project?

Thanks
WO
 
I've got a half-dozen NOS Westinghouse 1625s. They're a cool looking tube. After I've done a couple known builds, something like this may become interesting.

After spending the holiday weekend on a lake reading parts of Morgan Jones's "Building Valve Amplifiers", I'm pulling out the popcorn icon on this thread. I just love some of the colo(u)rful language in that book.

:lurk:
 
wildone said:
What iron are you going to use for this project?

Thanks
WO
Click to expand...

The output iron planned for this are from an old pair of Eico HF-22 that was field stripped. I'm still sourcing the power iron, but my buddy has a HUGE stash of parts, so I'll just go see him to get the power transformers.

I've gotten a lot of good feedback on the 807/1625 tube for audio. Looking forward to getting this up and running.
 
The ones I had were all NOS JAN from the end of the war. The RCA ones seemed ok, but the Sylvanias wouldn't run anywhere near where they should have. Blew a hole through the plate in one. There was a rumor that at the end of the war, a lot of tube makers did some shotty / tricky things to finish up the government orders. Some say that a lot of the 1625s got 6L6 guts. I have a whole sleeve of 6J5GTs that are actually 6SN7s with just one section hooked up. It was like they were clearing out all the mil. spec. stock. :dunno:
 
jaymanaa said:
The ones I had were all NOS JAN from the end of the war. The RCA ones seemed ok, but the Sylvanias wouldn't run anywhere near where they should have. Blew a hole through the plate in one. There was a rumor that at the end of the war, a lot of tube makers did some shotty / tricky things to finish up the government orders. Some say that a lot of the 1625s got 6L6 guts. I have a whole sleeve of 6J5GTs that are actually 6SN7s with just one section hooked up. It was like they were clearing out all the mil. spec. stock. :dunno:
Click to expand...

What date codes do yo have? The ones I can get sport a 1944 date code.
 
Thought I would bring this back from the inactive roster. It’s taken a lot longer that I thought, but it is ready for testing. I’ll post a couple of pics once it’s up and running.

I would up using 60W Edcor output transformers with a 6.6K CT. It is PP, with separate screen voltage regulation and fixed bias for each 1625. After talking this over with my friends, decided that a separate screen power supply was a safer way to employ the 1625 tubes. The front end sports a pair of 12SN7 tubes, and regulation is solid state (for now). I was able to get a dozen 12SX7 tubes for cheap, so I’ll try those out after the amp breaks in a bit. I’ve got about 28 RCA 1625’s on hand, so it should last a good while. :thmbsp:

Looking forward to trying this out once it passes the smoke test. :beer:
 
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