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tubelab SE 300b power transformer

Dhoff

Member
2008-02-08 5:30 am
I'm trying to find a hammond 300 series power transformer for the tubelab SE w/ 300b tubes. Any similarly priced alternatives are welcome.

Requirements are
640 to 650 v center tap at 150++ ma
5v at 3 amps (I might use a NOS rect. that needs more current than the 2amps that is required on the tubelab site)
6.3v at 4amps

Hammond makes a 300series supply which would be perfect, but I can't find it anywhere. I'd like to purchase from Angela, as they've got good prices (and I bugged him w/ a few questions, so want to repay the favor). If another vendor has a perfect match for me, I'll go w/ the match.

The angela universal doesn't have the current needed for the fillaments.
I was thinking of trying a hammond 372JX
300-0-300 w/ multiple primaries.
Would 600v C.T. be enough power for a 300b?
My other thought was to try using the 110v primary w/ my power which is closer to 120v. I don't know the math associated w/ transformers, so don't know how much that would raise the voltage on the 2ndaries.

Thanks for your help. I understand the rest of what is going on in these amp circuits, but I don't have much (any) experience with transformers or building power supplies.
 
I have been using surplus transformers in my 300B amps that deliver 640 VCT. My supply of them is getting low, so I am searching for a new source. Some users built 300B amps using the Hammond 276X transformer which is rated for 640 VCT. The problem occurs when some Hammonds put out far more than they are supposed to. I recently saw a 276X put out 708 VCT with a 175 mA load. The no load voltage was 740 volts. This caused some grief, and I can no longer recommend the 276X transformer.

Since Hammond transformers have a reputation for too much voltage, I have ordered a Hammond 272JX transformer for my next 300B amp. I couldn't justify the higher cost of the 300 series. I will test it as soon as it arrives, but I just ordered it yesterday, and it comes from the other side of the country.

I can assume that you are in the US, and have 60Hz power. If this is true you can get away with using the 110 volt tap on 120 volts to get a little more output (about 10%). The rectifier tube will see over 5 volts on its filament which could shorten its lifetime a little.
 

Dhoff

Member
2008-02-08 5:30 am
Thanks!
Are you going to try the 272jx soon after you get it, or is that a project for another time?

Do you have any trouble w/ the 200series from Hammond? The over voltage thing is an issue, but you came up w/ a good solution to that. I guess the other negative I heard about them was that they hum.
I really don't want a transformer that makes noise. This will usually be playing at a low volume.
 
Are you going to try the 272jx soon after you get it, or is that a project for another time?

There is a built TubelabSE board and two Edcor OPT's sitting on my bench waiting for it, so it will be tested ASAP. My work schedule doesn't allow for Tubelab work every day, but it will likely get tested on the weekend following its arrival.

Do you have any trouble w/ the 200series from Hammond?

I have used a few Hammond 200 series power transformers, and I have used dozens of the Allied 6K7VG and 6K56VG transformers that are essentially 200 series Hammonds only cheaper. They get hot which is typical of the 200 series. I have not had any of them buzz when used with a well designed tube rectifier circuit.

Other users do complain of hum, so it may be a real issue in very quiet environments. Most of mine went into guitar amps. I built at least 10 TubelabSE's using the little Allied transformer though and there was no hum issue.
 
When I got home from work today there was a box from AES on my doorstep. How long do you think that it took me to get sound from the moment I opened the box?

After dinner and an hour of mindless reality TV with Sherri, I ripped the box open at 9 PM and had sound at 9:34. I played the amp for an hour. During this time the transformer remained cool. It is a relatively cool (about 68 Degrees F) tonight, so the line voltage is up to 124.5 volts. I measure 372 volts of B+ with the 300 B's biased to 70 mA each. I had 390 volts on the hot side of the choke. With a more normal line voltage, I would expect 355 to 365 volts.

I didn't take any other measurements, I just wanted to listen.
 

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Dhoff

Member
2008-02-08 5:30 am
Have you worked with this transformer anymore? The initial results sound promising.
When you were running it, did it sound alright or would you rather be running the tubes a little hotter?
(to be honest, this is my first tube amp, so I won't know the difference no matter which transformer I get)
Thanks!
 
No, the amp hasn't been turned on since the initial test. I have been stuck at work until 7 or 8 PM this week. After I posted the initial report, I noticed that the 6.3 volt filament winding was puting out 7.2 volts. This is also a common complaint with Hammond transformers. The filament voltage is regulated in the TubelabSE, so the tubes are safe. The regulator however must eat this extra voltage causing it to generate extra heat. A larger heat sink is needed on the regulator IC.

I plan to do some more testing on this amp this weekend. I will be making a cabinet for it in wood shop class Monday night.

I think that this transformer is a good choice for 300B amps.
 
What are my choices?

I too have Hammond 272JX and a pair of 1627SEA OPTs. Plus I have a bunch of 50uF and 30uF motor run oil caps (both 370 V AC). I started to look into Tubelab SE amp and was wondering what my choices can be. I already have a pair of Sovtek 2A3 but am willing to try 45 or 300B if it means better sonics. By the way, I have 105db horn speaker actively bi-amped to cover 500Hz and up which is the reason why DC heater amp caught my attention. What would you recommend? Thanks.
 
I did some more experiments using the Hammond 272JX and a TubelabSE board. I found a bunch of 307A / VT225 tubes in my warehouse so I wired a pair in place of the 300B tubes and performed some testing last Sunday. It was unseasonably warm and my line voltage was 119 volts. B+ varied form 345 to 355 volts. Some prefer to operate 300B tubes with a higher voltage, and I usually tend toward running most tubes near their maximum voltage with a higher than "normal" load impedance. I would like to run 375 to 395 volts on 300B tubes, unfortunately there are very few transformers available that can make this voltage easilly. I have been using some surplus transformers that are 325-0-325 volts, but I am running out of them. The Hammond 276X or 273CZ (funny mounting) are marginal for current ratings if you crank up the tube current, and work but get quite hot. The 273BX puts out too much voltage, especially when the line voltage is high. The 372JX should be ideal since the "universal primary" allows for some fine tuning of the voltage, but this transformer is too expensive for my use.

The 300B tubes sounded good at 350 volts and I was planning to build a 300B amplifier using this combination.....until I heard the 307A's. I will build this amplifier, I just haven't decided whether it will use Chinese 300B's or vintage 307A's. The expensive 300B's are not in my budget.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=68216

The 350 volts that this transformer produces is too much for any "normal" 45's or 2A3's. The Hammond 1627SEA is a 2.5K ohm OPT. That is too low for a 45 tube, but is OK for a 2A3 or 300B. I am not familiar with Sovtek 2A3's, so I can't say if they can deal with 350 volts. The voltage could be lowered a bit by using a choke input, but I haven't tried this combination.

I have a friend who has 106db horn speakers that use active subs. Many of my amps have been played through his speakers. I have listened to all of his amps also. My favorite amp on his speakers is a TubelabSE using 45's (the Lexan amp). Unfortunately a 45 amp would require all new iron. He has a 2A3 amp that sounds nearly as good, but I don't know the details on that amp.
 
Boris_The_Blade said:
Hey tubelab (or anyone else), have you tried Edcor power transformers? I know they do custom jobs in small qty, and I almost bought a PT from them once, but the project got put by the wayside. If you have tried them, what are your impressions, any problems?

I somewhat recently purchased an Edcor PT for my SimpleSE that is being assembled. I should hopefully have some comments on it (along with the CXSE "Big Edcors") in the next few weeks at most. Keep in mind I haven't tried a whole lot else, so it will be less objective.
 
Hey tubelab (or anyone else), have you tried Edcor power transformers?

I have not tried any of the Edcor power transformers. I need to find a new source for power transformers to use in TubelabSE's with 300B tubes, but I don't have the funds or the time to investigate any custom transformers right now.

I plan to try a pair of their "guitar amp" OPT next.
 
I did have them price a custom one out for me at the time, i have no idea where my notes went for that but i know it was reasonable, something like only 20 bucks NRE.

edit: O, now I remember....I told them what I wanted, and they already had a part for it, it just wasn't on their website. I wanted a 5V heater tap, and they already had a design that was suitable...nice people to talk with too.
 
Edcor is great with customer service. The $20 fee only applies if they don't have something in their catalog. It is also a one time fee, so once you pay it anyone else can order that design for their very reasonable, standard price.

They have been very helpful on the phone, and I think the power transformer I ordered for my SimpleSE is almost a perfect match for the Hammond normally used in the design, since I believe the Edcors are rated for 120V primary and the HV tap is just slightly higher than the Hammond (which runs high anyway due to its primary rating).
 
The 307A amp has been on for 5 hours non stop tonight. I have fed it some vinyl (Simon and Garfunkle, and Al DiMeola) a CD, and 2 DVD's (Loreena McKennitt). I am now torturing it with Apocalyptica's Life Burns DVD at the clipping threshold. 4 cellos and a drummer can do some serious damage! Ever heard cellos played through guitar effects boxes?

The Chinese 300B's have been voted off the island. I will build the 307A version of this amp. The 272JX is the coolest running Hammond that I have ever met. It is just slightly warm, although it is hardly taxed in this amplifier and I usually run Hammonds much harder.
 
tubelab.com said:

The Chinese 300B's have been voted off the island. I will build the 307A version of this amp.

Hello,
How did you get the 5 pin socket so close to the PCB designed for the 4 pin? Did you use jumper wires, or were the pins(tabs on the socket) close enough that you could bend them to the correct contacts on the pcb?
I'm a tube nube.. I'm sure it would make more sense if I had ever seen a 5 pin socket in person.

I got a couple of "cheap" (but not really) Chinese 300b's for building the amp w/ the idea of replacing them w/ better tubes in the future. Not having to spend the hundreds on a pair of nice 300b's would be quite nice!!

My Hammond 272JX is on the way. I should have this thing powered up for the first time by the end of the week (or weekend).

Thanks.
 
The 5 pin socket that I used was a flat ceramic unit designed for mounting underneath a chassis and wired using point to point wiring. It is the only type of 5 pin socket that I have seen. This was one of those 5 minute experiments that I did to decide the fate of a box full of tubes sitting in my warehouse, so I simply sat the 5 pin socket on top of the 4 pin socket that is already on the PC board and ran wires to make the connections. The OPT (blue wire) is wired to the plate cap on top of the tube (green wire) and a 100 ohm resistor connects to the screen grid pin. That 5 minute experiment is now in its second week.

I have not decided just exactly how I will make this a permanent arangement yet. I mak make some sort of adapter using a 4 pin tube base and the 5 pin socket, or I may mount the 5 pin sockets above the board somehow and use short wires for the connections. I will post the details once I figure it out.
 

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