Recommendations for a 6k6 OT in UK / EU?

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pdf64
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Recommendations for a 6k6 OT in UK / EU?

Post by pdf64 »

I'm looking for an OT with a 6k6 primary for a JTM45 type build. I've actually got a real RS DeLuxe OT (6k6 primary) that I came across in a junk PA amp, but given their market value and rarity, I'm not comfortable overdriving the heck out of it. I'm using a 784-103 8k JTM45 type OT, built by Ingo Gorges, but the RS sounds better and puts out a little more power.
In a previous JTM45 build, I killed (shorted turns on primary) a Hammond 1650G 35W 200mA pri current 6k6 OT from their hifi range, which is a reason I'm stressing about the RS DeLuxe, as it's only rated for 30W and 125mA primary current.
Hence a search for a suitable 6k6 OT, but apart from INMADOUT or a Hammond 1650HA (40W hifi), there doesn't seem to be much else.
I expect a Trainwreck Express type OT would do fine, but can only find one from Tube Town.
I'm looking to sell the RS DeLuxe, once I've got something that sounds as good.
Any ideas?
Last edited by pdf64 on Thu Oct 29, 2020 6:18 pm, edited 1 time in total.
ChopSauce
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Re: Recommendations for a 6k6 OT in UK / EU?

Post by ChopSauce »

On a side note:

- aren't "Tube Town" transformers inMADout ones?
pdf64
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Re: Recommendations for a 6k6 OT in UK / EU?

Post by pdf64 »

ChopSauce wrote: Thu Oct 29, 2020 6:17 pm On a side note:

- aren't "Tube Town" transformers inMADout ones?
It looks that way
https://www.tube-town.net/info/datenbla ... jtm45D.pdf
http://www.inmadout.com/download/pdf/TUJTM45-3.pdf
Though the inMADout site doesn't list an Express type OT, as per the one sold by Tube Town
https://www.tube-town.net/info/datenbla ... twe-ot.pdf

I got the Ingo Gorges iron from Tube Town.
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martin manning
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Re: Recommendations for a 6k6 OT in UK / EU?

Post by martin manning »

pdf64 wrote: Thu Oct 29, 2020 5:22 pmI'm using a 784-103 8k JTM45 type OT, built by Ingo Gorges, but the RS sounds better and puts out a little more power.
KT66 power tubes? What does this OT sound like if you miss match and run a 4k primary?
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roberto
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Re: Recommendations for a 6k6 OT in UK / EU?

Post by roberto »

pdf64 wrote: Thu Oct 29, 2020 6:26 pm http://www.inmadout.com/download/pdf/TUJTM45-3.pdf
Though the inMADout site doesn't list an Express type OT
You can ask inMADout whatever winding pattern and impedance you want, he build every kind of custom transformers you need at reasonable prices.
pdf64
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Re: Recommendations for a 6k6 OT in UK / EU?

Post by pdf64 »

martin manning wrote: Thu Oct 29, 2020 6:44 pm
pdf64 wrote: Thu Oct 29, 2020 5:22 pmI'm using a 784-103 8k JTM45 type OT, built by Ingo Gorges, but the RS sounds better and puts out a little more power.
KT66 power tubes? What does this OT sound like if you miss match and run a 4k primary?
Doh, sorry, I prefer KT66 yes, my favourites are Groove Tube, Russian made I think, from the 90s. With probably 1000s of hours on them, they still put out slightly more power than a couple of pairs of Chinese ones (Tube Town and TAD) bought recently.
Power wise though, most of my 6L6 types put pretty much the same power under the same amp conditions.
I've not tried mismatching the current 8k OT up loud, and with the 2nd wave covid restrictions, it doesn't look like I'll get chance to do so (ie in the band context) for a few months.
On the bench, with a 8ohm load on the 16ohm tap, it puts out a bit less power still, compared to the intended loading.

Same with the RS DeLuxe, though it did try a mismatch on that (8 ohm cab on 16ohm tap), and didn't think it sounded as good.
It's worth noting that with the RS Deluxe, the reflected load changes from about 6k4 with a 16ohm load and the secondaries wired for 16ohms, to about 5k5 with a 8ohm load and the secondaries wiried accordingly.
On the bench, its power output is hardly any different either way.
It's all but impossible to compare the amp's performance with an 8 ohm, compared to a 16ohm, load. Though I've got a angled, closed back 4x14 and 2x12, both loaded with 8ohm G12M25. With the amp impedance set to match the cab used, the 4x12 seems a bit louder and more 'in your face' than the 2x12, but that's kinda to be expected anyway, and I don't think it can reasonably be ascribed to the different output tube loading.

For the record, with respect to its 6k6 primary (1 - 9), my RS DeLuxe's secondary ratios are 40.11 (A - F), 80.22 (C - B) and 80.22 (E - D).
A + going half wave at the '1' primary terminal results in + going half waves at the 'A', 'C' and 'E' secondary terminals.
https://valveampstuff.blogspot.com/2020 ... utput.html
roberto wrote: Fri Oct 30, 2020 9:20 am You can ask inMADout whatever winding pattern and impedance you want, he build every kind of custom transformers you need at reasonable prices.
I wonder if that's still the case, now that Savino has set up his own transformer business? eg was he their main technical design guy?
Oh look, his website has expanded, and has revealed another option :D http://www.savinoluce.it/index.php/guit ... 03v-z.html
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martin manning
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Re: Recommendations for a 6k6 OT in UK / EU?

Post by martin manning »

pdf64 wrote: Fri Oct 30, 2020 2:26 pmI've not tried mismatching the current 8k OT up loud, and with the 2nd wave covid restrictions, it doesn't look like I'll get chance to do so (ie in the band context) for a few months.
On the bench, with a 8ohm load on the 16ohm tap, it puts out a bit less power still, compared to the intended loading.

Same with the RS DeLuxe, though it did try a mismatch on that (8 ohm cab on 16ohm tap), and didn't think it sounded as good.
It's worth noting that with the RS Deluxe, the reflected load changes from about 6k4 with a 16ohm load and the secondaries wired for 16ohms, to about 5k5 with a 8ohm load and the secondaries wiried accordingly.
I don't know what plate voltage you're running, but 8k JTM45 with KT66 always appeared way too high to me, putting the screens at risk when overdriven. 4k would be more conventional, with the load line passing Vg1=0 a bit below the knee. Miss matching a 6k6 to 3k3 would be too low, IMO, probably making the crossing above the knee.
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roberto
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Re: Recommendations for a 6k6 OT in UK / EU?

Post by roberto »

Now I see why the inMADout site had issues few time ago.

Another Italian option is this one: a well prepared, very kind and a prompt guy.
https://shop.piemme-elektra.it/Categories/96
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roberto
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Re: Recommendations for a 6k6 OT in UK / EU?

Post by roberto »

martin manning wrote: Fri Oct 30, 2020 3:31 pm I don't know what plate voltage you're running, but 8k JTM45 with KT66 always appeared way too high to me, putting the screens at risk when overdriven. 4k would be more conventional, with the load line passing Vg1=0 a bit below the knee. Miss matching a 6k6 to 3k3 would be too low, IMO, probably making the crossing above the knee.
Just to bring some more italianity into the thread after the two trafo makers, this site is very helpful to exit from obvious and easily find new roads for loadlines:
https://www.vtadiy.com/loadline-calcula ... calculator

8 kOhm Raa is ok when the B+ is around 550V and screens at 300V, and you just hit the knee at g1=0 and plates at 70V.
Not a very common configuration indeed, even considering the drop on the screen resistors.
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