Power Transformer Identification

[Johnny_March]

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Hello. I looked to see if there are any other threads on this topic to avoid beating any dead horses. I found nothing so here goes…

I have a mystery power transformer. I don’t really have any info on what amp it came from because it was a homebrew amp that was poorly put together and dangerous to use. I wanted to see if I can use this for a new build, but I’m having a little trouble identifying this transformer.

The stamping on the bell reads: B-050438 EIA606–616. Search results say that this is the output transformer of a fender hotrod deluxe. I know the transformer I have is definitely not what that stamp says it is.

So the next action for me is to put a voltage through the primary and start identifying the secondary winding voltages. The problem with that is that I seem to have several wires on the primary side and I don’t really know which to put a voltage through. I can always do trial and error, but errors can be ugly in this sort of application.

Does anyone have any info on what the different striped wires could be on the primary side? If I followed the convention on power cords, black is hot (+) and white is neutral. There’s a black and white conductor, but I don’t think the same color code applies with transformer primaries. I wish all manufacturers followed the same color code convention, but it seems like the wild west with transformers.

I’ve attached a pic to show my transformer. Thank you so much in advance for your help.

[R.G.]

Use another, lower voltage transformer to drive it to avoid some of the uglies. If you're paranoid (and I am!) use a 12Vac transformer with a 12V car bulb in series just in case. The voltage ratios will still be the same.

[johnnyreece]

Sometimes, in my experience, the CT of the secondaries is on the primary side. I'd check to see if there's continuity between the green secondaries and the black/green stripe, as well as the red with the black/red strip.

[Stevem]

Well it’s not a HR Deluxe OT like the bell states, and it’s not that same amps power transformer either since one for a HRD has only 6 wires.

The best way to proceed to test it out would be with a small AC wallwart, or if you have another amp jump in the 6.3 volt filament voltage.

[Phil_S]

Sorry, this is going to be a long post. I hope it's worthwhile.

606 is a Woodard Schumacher transformer. It is possible this was sourced by Fender, but that is neither here nor there. I've tackled this problem before. The voltages can be sorted out. It is the current (amps) capacity that is challenging. The only sure way to know the amperage capacity is to run it until it lets the smoke out and we don't want that to happen.

The PT has 5 wires on the primary. For starters, I'd assume white is common. If this is right, your meter will tell you the rest. Check for ohms between white and each of the 4 wires. The one with the greatest Ohm reading is for the highest input voltage and the one with the least Ohms is for the lowest voltage input. If I had to guess, I'd say this is an "international" transformer, with inputs for 100V, 115V, 220 or 230V, and 240V. (100V is for Japan.) Whichever primary combination gives you close to 6.3V on the filament winding (probably the green pair) will tell you what is the appropriate choice for whatever is your wall voltage. From there, you will also know the output on the other windings. I'll guess brown is for a 5V rectifier, and the three blue ones are a center tapped filament winding.

I'll assume you are the US/Canada. Because this is an older transformer -- date code 616 suggests made 16th week of 1966, it may have been wound for 110, 115, or 117V on the primary. Because line voltage is commonly at 120V or higher, expect the filament winding to produce more than 6.3V -- maybe as high as 6.8V or more.

Getting the VA rating, from which you derive the secondary capacity is more of a challenge. Knowing the DCR on each winding is a good place to start. There is a chart someone gave me many years ago, but I can't vouch for it's accuracy. If you really want to get into it, it is necessary to put a load on the secondary. Here is something from a random Google search: https://electronics.stackexchange.com/q ... econdaries

Here the chart I was given:

mA Rating of Unknown Transformer

From the Primary Winding
For a 120 volt AC supply the VA rating and primary resistance is as
follows.
30 VA = 30 to 40 ohms
50 VA = 13 to 16 ohms
80 VA = 7 to 9 ohms
120 VA = 5 to 6 ohms
160 VA = 2.5 to 3.5 ohms
225 VA = 1.8 to 2.2 ohms
300 VA = 1.0 to 1.3 ohms
500 VA = 0.45 to 0.55 ohms
Simply multiply all ohmage values by four (4) for a 230 / 240 volt supply.
Derate to 65%, which is probably reasonable and to allow 15VA for the filament windings.

From the Secondary Winding
One very general way, based on a copper loss of say 4%. The ht winding rating is probably the most important. Find the secondary voltage, e.g. 300Vac. Take 4%, giving 12V. Measure the winding resistance; one half if 300-0-300V (i.e. a 300V winding), if bridge then the whole winding. The current will now be that which causes a 12V drop across the winding d.c. resistance. Thus dividing 300V by the resistance would give a ball-park figure for current (Ohms Law). Heaters more difficult; same method, but low voltage winding resistance is usually impossible to measure accurately. The heater current could be expected to be in line for the output stage that would require the previously calculated anode current.

One degree further would entail loading of the transformer. Sometimes this is possible with mains globes. Such a load across the ht winding for >1 hour should cause the transformer to get only slightly warm, as you still have no heater load, unless you simulate that too. Very generally heater and h.t. load can be assumed to have similar power figures.

Finally, I found a bit of free software years ago that provides a calculation based on various measurements. I don't know where I got it or how I could transfer it to you. I'm posting a screen shot that shows the inputs required. If you can give me the data, I can run the calculation for you. Again, I don't know the quality of the result, but, at least it's something and I suspect it's at least pretty good.

[thetragichero]

if that's just a simple win32 program you might try compressing the directory it's in and uploading the zip. i'd certainly be interested in trying to get that to work in wine (psud and tsc seem to work so that's all i really care about)

[Johnny_March]

Ok, so quick update. I decided to pull the bell cover off this transformer. Someone has been messing around here. When I pulled the bell cover off, it uncovered another code that is stamped onto the copper band that is surrounding the paper on the transformer. That code is 039044 EIA606 208 SB4. I trust this number more.

Looks like tubeampdoctor has this one. I guess there are two pairs of 120V primary windings; one of them has a white center tap. If you hook up blk/grn to blk/yl you can use blk/rd and blk for 240V.

The secondaries are funky. There’s a 45V and a 19V winding there and the high voltage is 315V with no center tap. I guess this means I’d only be able to go after a fender champ design with an SS rectifier.

What does everyone think? Is this worth it?

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[thetragichero]

2.5A filament current. think BIGGER. 3 or 4 little bottles with 2x6v6. could probably swing 2 preamp tubes and 2x6l6. full wave bridge rectifier. you've got a handy bias winding too for fixed bias. the world is your oyster

[martin manning]

All you need to know is here: https://ampwares.com/schematics/champ_25_se.pdf

[Stevem]

Great detective work Martin, you nailed it!

It was my guess that the blue wires where for a SS IC driven section of whatever amp, just was not sure!

[Phil_S]

2.5A filament current. think BIGGER. 3 or 4 little bottles with 2x6v6. could probably swing 2 preamp tubes and 2x6l6. full wave bridge rectifier. you've got a handy bias winding too for fixed bias. the world is your oyster

+1 on this idea. It looks like the limiting factor is the filament supply at 2.5A. At 180mA this PT will power a pair of 6L6 but that will limit you to just 2x 12AX7. If you want something with a little more to it, go with the 6V6's.

I really like the way the made the primary. I was thinking the worst, that it was one long winding. Split as 2 windings allows the builder to wire in series or parallel to use the full capacity.

[Phil_S]

if that's just a simple win32 program you might try compressing the directory it's in and uploading the zip. i'd certainly be interested in trying to get that to work in wine (psud and tsc seem to work so that's all i really care about)

It is a rather small size folder. I wasn't really thinking about where I could make it public. I realized this morning I can put it on onedrive live so that anyone with the link can see it. Here's the link. It expires on October 17 at which time I'll delete it. I don't like leaving such an open access.
https://1drv.ms/u/s!Atnmnqus05tDg8lt3q_ ... A?e=TbrXwa

[martin manning]

It looks like the limiting factor is the filament supply at 2.5A. At 180mA this PT will power a pair of 6L6 but that will limit you to just 2x 12AX7. If you want something with a little more to it, go with the 6V6's

With limited use of the 19-0-19 winding it might be ok with 2x 6L6 and 3x 12A_7

[Johnny_March]

Ok, well if I can do 2 6V6's then I'm thinking I could build a fender deluxe 5E3 circuit. I haven't built one of those yet

[Phil_S]

A 5E3 is a different kind of amp. I built one and didn't like it. Then, I built it again and still didn't like it. I thought maybe I'd built the first one wrong. This is just personal taste. We know this circuit is well liked by many. I recommend playing one if you haven't already or, not as good, search youtube for samples.

Also, it's a bit of a waste of the 180mA capacity. A 5E3 would be nice with half that or a little less. I think it might be a little "stiff." As I understand it, part of the 5E3 charm is it's sag. I think I'd look at a 5B6. You'll need to do it with ss rectifier, but I don't think that matters much. Whatever, there are lots of possibilities. Just my 2¢. Good luck with it.