Selmer/Kelly Transformers

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Selmer/Kelly Transformers

Postby LD50 on Sat Apr 08, 2017 9:18 pm

I thought this might get more chance of someone having the info on this here rather than in the component section.

I have two output transformers for projects:
One is from a Selmer TnB 100. It has the same core physical size as my spare Marshall JMP 50 transformer but is open frame with a brown perforated bobbin looking very much like a Partridge with the yellow lacquer.
It has T214 stamped in white print on the frame and the primaries are red-black-orange measuring 36.5ohms anode to anode (Marshall Drake 784-139 is 83.5ohms).
It has Black-Green-Brown-Yellow secondaries but I am unsure of the hook up. I think black is common and I get 0.6ohms black to green, 0.5ohms black to brown and 0.4ohms black to yellow, so I m hoping that they are 15. 7.5 and 3.75 taps respectively?
Can anyone confirm that and, before I have to make up a low voltage test transformer does anyone know the primary impedance of this?

Second is from a 100w Kelly (model I do not know. It is the same physical size as my spare Marshall 100w OT (Dagnall C2668) but is again open frame with paper but no cheeks on the bobbin. It has the number T198 in white hand script on the paper. The primaries are again red-black-orange measuring 36 ohms anode to anode (vs the Dagnall that is 30 ohms)
The secondaries are again, Black/Green/Brown and Yellow (Black being innermost, yellow the outer in the layering. Black to green is 0.1ohm, Black to Brown is 0.2 ohm and Black to yellow 0.3ohm. (but I know the Dagnall common is brown)
Can anyone confirm the hook ups for this OT and know it primary impedance?

I am building an Orange OR 100 clone and have all the parts. I was going to rob a Dan Armstrong of its Partridges but it seems a shame (and the PT has 600v B+) and I propose using the most suitable of these transformers. For this.

TIA.
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Re: Selmer/Kelly Transformers

Postby Mr. Foxen on Sun Apr 09, 2017 2:38 am

Bunches of inside shots of Kelly's here, might be able to follow the wires round: https://ampstack.wordpress.com/?s=kelly&submit=Search
New music: https://warriorpope.bandcamp.com/album/anchorite
Gear tinkering blog: http://ampstack.wordpress.com/
Made a Facebook page for my ampguts stuff. Feel free to come post amp guts and rig shots: https://www.facebook.com/pages/Ampstack/351966881575839
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Re: Selmer/Kelly Transformers

Postby trobbins on Mon Apr 10, 2017 8:00 am

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Re: Selmer/Kelly Transformers

Postby LD50 on Mon Apr 10, 2017 3:48 pm

Thank you for the photographs of the Kelly on your blog, it does confirm that black is the common, guess I will have to get a signal generator to measure what is going on for sure.

Also thanks to the Vintage Hofner site, I have those schems already. It reassured me that the smaller OT (T214) is actually a 100w transformer! Shame no wire colours. Also interesting that the T198 has 100v, 15, 7.5 and 3.75 taps and electrostatic screen when mine only has the conventional taps and screen, maybe two versions of the T198 for PA and guitar use?

I also have some vintage trannies of the right size from KT88 and EL34 amps but they have UL taps too.
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Re: Selmer/Kelly Transformers

Postby trobbins on Tue Apr 11, 2017 6:30 am

Doing a quick connection of a half-primary winding to a small 5,6 or 12VAC transformer, and measuring the other half-primary and the secondaries, gives reassurance of not only the tapping wire colours, but also that the OT is still 'good to go'. A quick calculation from those voltages also clarifies the primary PP impedance, as you are now pretty certain of the secondary winding impedances. Posting results will also help those in the future :thumbsup:
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Re: Selmer/Kelly Transformers

Postby LD50 on Tue Apr 11, 2017 6:02 pm

trobbins wrote:Doing a quick connection of a half-primary winding to a small 5,6 or 12VAC transformer, and measuring the other half-primary and the secondaries, gives reassurance of not only the tapping wire colours, but also that the OT is still 'good to go'. A quick calculation from those voltages also clarifies the primary PP impedance, as you are now pretty certain of the secondary winding impedances. Posting results will also help those in the future :thumbsup:


Yes I will
Just ordered a proper signal generator so I will wait until I get that and then put a scope on the secondaries too.

Got this info from Majestic but these are turns ratios:

• T214
o (A) 100 (B)
o (orange) 530 (black) + 530 (orange)
o (A) (black) 50 (yellow) + 21 (brown) + 29 (orange) (B)

• T198
o (X) (black) 116 (A)
o (Orange) 615 (B)
o (A) 312 (blue)
o (black) (B) 615 (Red)
o (X) (Black) 58 (Green) + 24 (Brown) + 34 (Yellow) (A)
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Re: Selmer/Kelly Transformers

Postby pdf64 on Tue Apr 11, 2017 10:35 pm

LD50 wrote:...Just ordered a proper signal generator so I will wait until I get that and then put a scope on the secondaries too...

I think it may be better to put a much bigger signal on to the windings than can normally be supplied by a regular signal generator.
Why not just connect the primary across the mains (ideally via an isolation transformer)?
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Re: Selmer/Kelly Transformers

Postby trobbins on Wed Apr 12, 2017 12:00 pm

Things could get ugly quickly if the OT had some technical fault, and the supply voltage had a high current capability, or a mistake was made with connections. Most diyers would have circa 12Vac available, and there is no extra benefit from a high voltage supply, or a sig gen if turns ratio and nominal PP impedance is the target measurement.
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Re: Selmer/Kelly Transformers

Postby pdf64 on Wed Apr 12, 2017 10:28 pm

My band:-http://www.youtube.com/user/RedwingBand
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Re: Selmer/Kelly Transformers

Postby trobbins on Thu Apr 13, 2017 12:58 am

Yes it's sad that one could take away advice that 400 VAC could be applied to the OT for testing as that is what happens in situ. 400Vac sort of implies a 560 Vpk signal swing, implying at least a 650Vdc B+.

Why add safety and damage risk for a simple turns ratio measurement.
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Re: Selmer/Kelly Transformers

Postby pdf64 on Thu Apr 13, 2017 8:19 am

trobbins wrote:Yes it's sad that one could take away advice that 400 VAC could be applied to the OT for testing as that is what happens in situ. 400Vac sort of implies a 560 Vpk signal swing, implying at least a 650Vdc B+...

I don't understand the reference to 400Vac?

trobbins wrote:...Why add safety and damage risk for a simple turns ratio measurement.

Understanding and mitigating the hazards of messing with electricity is a pre-requisite.
I'm a big fan of safe working practice, eg argue strongly against current shunt plate current measurement as its generally less accurate and rather more hazardous than other methods; so yes, it seems bad practice to choose hazardous methods over others, when no benefit accrues.

But as someone with a deep understanding of the issues advises that OT ratio measurements made at a low excitation voltage may be inaccurate, then, given sufficient competence and resource, there may be sufficient justification to use a suitably high excitation voltage.
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Re: Selmer/Kelly Transformers

Postby trobbins on Thu Apr 13, 2017 11:44 am

Cerrem's comment was:
"For this type of transformer measurement...
You need to get up and out of the mud..... 2V is way to low on the BH curve for that low quality steel..
Keep in mind that the real operating voltages are up around 400V AC range......"

I suggest his concern was the OP driving the secondary low impedance winding. A simpler measurement is to drive a half-primary and have a voltmeter that can acceptably measure the voltage coupled to the secondary.

But the throw away reference to 400Vac was a poor value to note - maybe a typo.
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Re: Selmer/Kelly Transformers

Postby LD50 on Thu Apr 13, 2017 2:22 pm

It is an interesting discussion.

I simply hoped someone might have the wiring colours to hand.

I am a big boy and can safely measure with respect to voltage (my Fluke or AVO Mk VII will both cope) and calculating the ratios, just a bit busy but may get some time this Easter w/e.

I bought the signal generator as I wanted something more practical than the Sig Jenny programme I was using on line for general debugging.

I've got a tranny knocking around with a 100vac tap that will work quite nicely for these purposes (and as per Mr Merren's suggestion move on up the hysteresis loop curve a little.

I promise to post back with pictures and numbers as soon as I can.
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Re: Selmer/Kelly Transformers

Postby LD50 on Sun Jun 25, 2017 10:04 am

As promised I will update with data from my testing.

I applied Voltage turns ratio = Vin/Vout with 35vac in

Impedence Ratio = (Vin/Vout) squared x putative tap = ratio.

eg For 16 ohm tap, 35/3.35 = 10.45

10.45 squared = 109.16

109.16 x 16 =1746.49 ie 1.75k

Using this method

The T198 comes out as a 1.75k transformer with:
Black - common
Green - 4 ohm
Brown - 8 ohm
Yellow - 16 ohm

The T214 comes out around 1.8k
Black - common
Green - 4 ohm
Brown - 8 ohm
Yellow - 16 ohm

I also used this on some unknown OTs I had lying around and found a Drake (model number unknown) to be 7.2k and another at 6.6k (both of JTM45 size,weight and mountings) so both potentially useful later.
I hope the info on the Selmers 100w trannies above comes in useful for someone.
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