JTM45ish transformer orientation

[dcribbs1412]

Marshall amps have the PT OT then choke
I see Fenders with the PT choke OT
wondering if putting the choke between PT and OT would be a problem
on a JTM45ish build...I read places it's OK but wanted to check here.
was thinking of mounting like this

pics
http://i1018.photobucket.com/albums/af3 ... m45001.jpg
http://i1018.photobucket.com/albums/af3 ... m45002.jpg

any comments are greatly appreciated

Thanks

Darin

[Cliff Schecht]

The choke goes in the same orientation as the PT and the OT still gets rotated by 90 degrees either way. Since the choke is feeding into push-pull stages and has a lot of decoupling around it anyways (i.e. it's part of an LC lowpass filter), it's less susceptible to hum than the OT. Also this way the choke can act as a shield between the PT and OT.

[dcribbs1412]

Thanks Cliff
I'll rotate the choke to match PT and rotate the OT 90

[M Fowler]

I noticed a difference with kits around the net running different HT voltages in the PT and even different OT primary ratings for KT66 type.

Why such differences? What is the correct PT and OT for a JTM45 with KT66's.

Mark

[dcribbs1412]

Good question Mark
I've seen 600V-700V PT's Martrans,MM,Triode...they all have one each a little different.
not sure what the "correct voltage" is.....just guessing around 680V-700V...kinda why I got the PT I did
has 680VCT, 644CVT, or 580VCT @ 210mA DC to experiment a little
with KT66's and 34's maybe even 6L6's and 6V6's
I am going to use a 8K OT
I hope it turns out decent

Darin

[ToneMerc]

I noticed a difference with kits around the net running different HT voltages in the PT and even different OT primary ratings for KT66 type.

Why such differences? What is the correct PT and OT for a JTM45 with KT66's.

Mark

Mark, the original Radiospares OT that were in the early JTM45 had tag board terminals for at least 3 different impedences, my understanding is that most were either wired as 6.6K or 8K. The 66' that I worked on was wired as 8K and had about 465V on the plates. Many have observed stock voltages in the range of 440V-470V. However, many like the tone of the softer voltage clones at around 390-410V and of course these are much easier on tubes.
Personally, I think the softer voltages are too bassy and this is why many will change the PI couplers to .047 or even .022 instead of the stock .1 value. When I built my clone I stuck with all the stock values, 8K and hit the plates with about 445 volts.


https://tubeamparchive.com/viewtopic.ph ... hlight=jtm

FWIW, the KT66 sounds good at it's mistaken load of 6.6K or 8K and also at 3.4K as well.

TM

[The New Steve H]

I built a 5F6A clone with the choke between the transformers, and it sounds great. None of the laminations are in the same plane.

[M Fowler]

Darin & TM,

Thanks for the feedback I would like to go around 450v and still not sure about either the 6k6 or 8k.

Using 6k6 makes more sense to me and don't quite understand going with 8k other than to lower the power amp output for tone factor.

Still time to ponder

Mark

[ToneMerc]

Darin & TM,

Thanks for the feedback I would like to go around 450v and still not sure about either the 6k6 or 8k.

Using 6k6 makes more sense to me and don't quite understand going with 8k other than to lower the power amp output for tone factor.

Still time to ponder

Mark

It's really a personal taste of whether you like 8K or 6.6K. If you want the look at a decent price, I would suggest Brian's JTM45 PT.

http://marstran.com/JTM45%20Transformers.htm

I have a new one that I was going to use for a higher voltage JTM50, but I ended up getting a Merren JTM50 PT instead. I may put the Marstran up for sale soon and I have the english bracket for it as well.

TM

[dcribbs1412]

TM
thanks for the link to your Recent JTM45 Build
really really nice...amazing collection of parts...
wondering about the KT66 tubes
do you have any suggestions for tubes...new production?

Thanks

Darin