Need OT specs for 5F6A Bassman

[M Fowler]

Oh those darn Canucks

[FunkyE9th]

I know, it's just a pet peeve I have.
Sometimes people will offer suggestions only to find out later in the thread that the OP lives in Kazakhstan.

\

I just assumed SRV is from Austin.

[Phil_S]

It's a big country. Maybe you live in Whitehorse, YT? Hmmm.....bought some used transformers (dated 1966) from a guy up there once. Absolutely rust free. There must be almost zero humidity there.

[tribi9]

I live in Ontario. In a city called Kitchener. One hour west of Toronto. Not sure about the zero humidity here tho' it is freaking humid in the summer. In fact too freaking humid sometimes.

[srv]

Hello!

I have been out of town and just got back, therefore I didn't get the chance to drop by in the last couple of days. I live in Eastern Europe, not in a wealthy country... significant shipping cost to order a tranny from the states and additional expenses like VAT tax and duty throw me way over my budget which is small to begin with. I looked over and over on the net, but couldn't find a decent guitar tube output transformer blueprint beside the "the primary is X kohm and the secondary is Y ohm, it's Z watts" description I already knew.

I need EI core dimensions, wire thickness and number of turns, diagram of interleaving the windings, etc. I found some stuff for Hi-Fi, but that's quite different requirements than guitar amps so I would appreciate some advice.

Please, if anybody who can help in any way is reading this, please contact me and help me out a little bit, I'd be very grateful. It doesn't have to be a bassman OT, just something that sounds good in a push-pull guitar amp.

Thanks in advance!

[flood]

i totally feel your pain... i wanted to get output transformers wound from a local manufacturer who was famous for his trannies back in the heyday of tube radios. spoke to him for about half an hour trying to convince him to build me 5 OTs... but he said he simply couldn't do it cause he doesn't have the technical specs for winding OTs anymore, none of the employees of that period work there anymore and all the books and diagrams are missing or were disposed of after the transistor age took over. i'd have to get him a sample, which he would then reverse engineer destructively....

[Noel Grassy]

srv & flood,
Welcome to the Amp Garage. I'm under the impression none of the folks reading this thread actually have the data you require.
Everybody worth a hoot are quick to come to the aid of even the most outrageous request. That said, might I suggest dropping the same request at sites like Gerald Weber's Kendrick Amps, Ted Weber's site & any of the other suppliers here in the US. Tell them of your desires and indicate where you are in the world (re-inforcing how
you are no threat to their livelihood and are not competition in any way) and see if they respond positively. Gerald Weber has an intimate knowledge of the early tweed Fender amps and I suspect he'd be willing to give you the OT data no problem. Perhaps Pacific or Heyboer are worth asking as well.

I wish I knew but I only go back to the Brownface Bassman 6G6-B. Thankfully the OT in that amp is still alive.
Here's some links to the above mentioned entities. Best of luck.
www.kendrick-amplifiers.com
www.tedweber.com
www.pactran.com
www.heyboertransformers.com

Noel Grassy.

[flood]

I'm under the impression none of the folks reading this thread actually have the data you require.
Everybody worth a hoot are quick to come to the aid of even the most outrageous request.

that's very true which is why i love this forum to death! practically everything i know about tube amps was learned here....

i can imagine the data being extremely difficult to have in the first place. thanks for the tips though - maybe i'll just go right ahead and do that, but i think it would be more effective if i actually reverse an OT - even a dead one would do. over here, people work better with the acutal thing in front of them than with data. will scour the ebays.

[martin manning]

The thing to realize is that this information has commercial value. The companies that make these things are in it for profit, and revealing their proprietary data and methods, especially knowing that it will be passed directly to an off-shore manufacturer who might be able to produce competing parts at low cost, is not in their best interest. Even if the specs were obtained through reverse-engineering, that represents an investment, and I'd be surprised if it would be freely given away. No emotion involved on my part; this is just the reality of it.

MPM

[flood]

The thing to realize is that this information has commercial value. The companies that make these things are in it for profit, and revealing their proprietary data and methods, especially knowing that it will be passed directly to an off-shore manufacturer who might be able to produce competing parts at low cost, is not in their best interest. Even if the specs were obtained through reverse-engineering, that represents an investment, and I'd be surprised if it would be freely given away. No emotion involved on my part; this is just the reality of it.

MPM

very true... in these times, i'm don't think anyone would want to divulge a proprietary secret of that sort. i can live with that, i think.

[srv]

The thing to realize is that this information has commercial value. The companies that make these things are in it for profit, and revealing their proprietary data and methods, especially knowing that it will be passed directly to an off-shore manufacturer who might be able to produce competing parts at low cost, is not in their best interest. Even if the specs were obtained through reverse-engineering, that represents an investment, and I'd be surprised if it would be freely given away. No emotion involved on my part; this is just the reality of it.

MPM

Very true, even though the information can be obtained through reverse-engineering. In modern times, I've seen electronics sealed up in hard epoxy to prevent reverse engineering without significant effort and unavoidable circuit destruction. When tube circuits are in question, it's hard to prevent reverse engineering, but nevertheless the manufacturers being most copied from are still in business and have a brand stronger than ever as well as the sales. Their business model (or at least that's my impression) isn't based on unavailability of information which only they possess, but rather on high quality materials, machinery and skills used to make the product.

That being said, I still believe that even if some of these guys helped me out with some more detailed information without revealing all their tricks, I still wouldn't have neither the capital, the large scale manufacturing skills or advertising potential to even think about jeopardizing their business. People who do, also have the resources and expertise to do a proper reverse engineering, and e.g. a Chinese manufacturer would quickly learn the proper way of making them. This is not a mass production item you make in gazillions, so people, the customers, faced with a choice still prefer American made brand and quality over a third world country knock-off of questionable performance for a mere savings in price. Anyway, that's just my humble opinion...

[Phil_S]

I think that you really are dealing with trying to unlock trade secrets here. No one wants to reveal how they put the mojo in the tranny because the very day they do it, someone will be producing it in a developing nation for 10% of the cost, selling it for double the profit, and undercutting the price by at least a factor of 2, as well.

Even so, much has been written on the subject and it should not be too difficult to guess and make something close. One thing you might get someone to do for you is to measure the outer dimensions of the laminations, and that will give you a really good idea of the rest. If you are a little off spec, do you really think anyone will know or care? Maybe, or maybe not.

I found this at the 18W forum for winding an 18W Radiospares reproduction. Maybe you can use this information as an example to model a Bassman OT of your own design. I am willing to suggest that if can find someone to give you just a little bit of information, it would go a long way. Also, bulking up this design for a "36W" might be pretty close and worth a try.

Radiospares reprod. OT

Iron dimensions 78X67X25mm(60-70's Europe standard)
Cold rolled grain oriented silicon iron.
Lamination thick 0.35 mm/29 gauge.

Primary turns 3030 (1515- CT- 1515)
Secondary turns 136

Primary wire (bare) 0,18mm
Secondary wire(bare)0.71mm
------------------------------------
3030:136=22,2 turns ratio
impedance ratio(square of turns ratio)=496,3

Secondary taps:
4 ohm @68 turns =7,941K
8 ohm @96 turns =7,968K
16 ohm @ 136 turns =7,941K
--------------------------------------
Interleavings:

primary1 ----- 863 turns
secondary1 ---- 68 turns (end 4 ohm tap)
primary2 ----- 863 turns
secondary2 ---- 28 turns (end 8 0hm tap)
primary1" ---- 652 turns
secondary3 ---- 40 turns (end 16ohm tap)
primary2" ---- 652 turns
-----------------------------------------------
If you find suitable old silicon iron,and carefull at winding you'll have realy good OT as RS.
Tried and tested icon_wink.gif
Prespan paper is not standard wax paper,it's mineral oil/ treated or shellac treated paper.
You can made transformer/capacitor paper if isn't avaiable.
If you don't have vacuum tank for soaking trafo in varnish,you can lacquire wire with shellac after every row is finished.
Don't forget margins when you wind,and to isolate side of bobbin prior to assembling of laminations.

[alanp]

Very true, even though the information can be obtained through reverse-engineering. In modern times, I've seen electronics sealed up in hard epoxy to prevent reverse engineering without significant effort and unavoidable circuit destruction.

Some of the old ARP 2600 synthesizer modules were potted to keep down temperature drift in the components as well, weren't they?

[srv]

I think that you really are dealing with trying to unlock trade secrets here. No one wants to reveal how they put the mojo in the tranny because the very day they do it, someone will be producing it in a developing nation for 10% of the cost, selling it for double the profit, and undercutting the price by at least a factor of 2, as well.

You are probably right, it's just like WD40, which was never patented in order to avoid disclosing the formula. Even though I am still one of the sceptics who don't believe electronic components can have a soul or mojo, only measurable parameters and work nicely when chosen correctly. Good tube amps don't come cheap and they are all about the sound. That's why people still stick around with this vintage technology. Therefore, I sincerely doubt anyone would ever pick a Chinese OT (just for the record, no offense to any Chinese people reading this) over the one made in USA by an experienced and skilful company to save 40-50$ in a 1500$ amp. If I didn't have to pay triple to have it shipped here, I would also get one that's quality made with experience in the USA instead of having it custom made.

I found this at the 18W forum for winding an 18W Radiospares reproduction. Maybe you can use this information as an example to model a Bassman OT of your own design. I am willing to suggest that if can find someone to give you just a little bit of information, it would go a long way. Also, bulking up this design for a "36W" might be pretty close and worth a try.

I don't know how to thank you, believe it or not, this is the only example of useful specs I've seen online for a guitar amp OT. If I don't find any more info, I'll probably try to work out which calculation gives me the closest results to your specs, and then apply it for a 45W JTM45 or Bassman.
If you were closer, I would buy you as many beers as you could drink! People are very helpful on this forum, I thank you all!

[Jana]

Have you tried finding a transformer at a junkyard, an electronics surplus shop, anywhere? The Russians used tubes in their equipment for a much longer period of time than the US. They also used a lot of 6L6/5881 tubes. There should be transformers around to be had. Sovtek amps? Military amps?

I agree that no one is going to just hand over the intimate details of a 59 bassman transformer to you. Ask for their bank account number instead.

With physical dimensions, which you can find easily on the web if you look, and some basic specs such as wattage, impedances/turns ratio, a competent transformer winder should be able to create a suitable 50W OT for you.