5F6A build transformer question...

[chikov]

Hello. I am getting ready to build from scratch Bassman 5F6a amp but I need to buy OT and the choke for it. The problem is that I’d like to get one with multiple speaker Impedance (4,8,16 ohms). I did some research and found the one the looks right, but I am not sure. On tubesandmore.com it is
P-T1760L (see photo).
I also did some reading on chokes and got confused. They say that it should handle about 150 mA current, but the one on schematic can handle only 90mA, is it right? Which one should I get then?
I’d appreciate if anyone could help me with this, thanks.

[martin manning]

1760L OT and 90 mA 194B choke will be fine for a 5F6-A.

[chikov]

Thank you!

[Stevem]

That’s not the OT you want!
The 1760l is for back and silver face amps and is not interleaved like the original Triad OT, you want the 1650N for a tweed 50 watt build.

[ChopSauce]

That's interesting! That line of Hammond products seem to be very good. Maybe a good alternative for us leaving in Europe, who can't always afford the cost of high quality made in US, due to taxes and shipping costs...

The 1650N nevertheless does not seem to offer a convenient way to switch between speaker impedances, if that is mandatory.

Hammond http://www.hammondmfg.com/guitarLineOT.htm lists the 1760K as the part for the tweed bassman, which should offer a more convenient way of switching between impedances ... at the cost of tone?

[chikov]

I ended up getting 1760K one. It has all the outputs I need.
Thanks for all your help. I will stay in touch.

[pdf64]

…The 1760l is for back and silver face amps and is not interleaved like the original Triad OT, you want the 1650N for a tweed 50 watt build.

What are the differences in their interleaving patterns?

[martin manning]

That’s not the OT you want!
The 1760l is for back and silver face amps and is not interleaved like the original Triad OT, you want the 1650N for a tweed 50 watt build.

I will disagree there. 1650N is a Hi-Fi transformer, and requires rearranging the secondary windings to change its impedance ratio, as chopsauce points out.

Chikov wants an OT that has 4, 8, and 16 ohm secondaries, so the Blackface Bassman 1760L OT is the way to go.

Hammond has three options specifically designed for the 5F6-A:
1750K, listed as being for Tweed Bassman (the original), which has a 2 ohm secondary, or the multi-tap 2, 4, 8 ohm version, 1760K.
1750KA, listed for '59 Bassman (the reissue), which has a 2 ohm secondary for the 4x10 combo, and is probably electrically the same as 1750K.

All 4 of these are very close in price, suggesting that there isn't any significant difference in the winding patterns.

That's interesting! That line of Hammond products seem to be very good. Maybe a good alternative for us leaving in Europe, who can't always afford the cost of high quality made in US, due to taxes and shipping costs... :?

A very good option for EU, IMO.

[sluckey]

The 1650N nevertheless does not seem to offer a convenient way to switch between speaker impedances, if that is mandatory.

Yeah, I have one of that series (1650L) in my AC-15. You can strap the secondary to easily provide 8Ω and 16Ω outputs, but not all three choices.

However, FYI, Hammond has a new and improved version for the 1600 series and they do have an easy straight forward secondary wiring. In this case the part number would be 1650NA. Here's the datasheet...

https://www.hammfg.com/files/parts/pdf/1650NA.pdf

[didit]

Hello --

Or use a rotary switch per the helpful diagram posted in this thread (and elsewhere).

https://ampgarage.com/forum/viewtopic.php?t=34500

Best .. Ian

[Stevem]

All of the tweed era Triad made OTs used in the 2 or 4 6l6 tubed amps where interleaved, yes like top shelf mono block Hi Fi amps of the day.
When Fender switch to Schumacher made OTs the interleaving went by by!

[martin manning]

All of the tweed era Triad made OTs used in the 2 or 4 6l6 tubed amps where interleaved, yes like top shelf mono block Hi Fi amps of the day.
When Fender switch to Schumacher made OTs the interleaving went by by!

I have read that the Triad OT's were good quality audio transformers, but interleaving is not an all or nothing thing. The later ones most likely have interleaved windings, but perhaps not as many sections. Does that matter? The purpose of interleaving is to lower leakage inductance and interwinding capacitance to preserve high frequency response. The Hammond data sheets indicate bandwidth extends to 15 kHz for all of the Bassman replacement part numbers above, so whatever they are doing seems to be adequate considering the speaker response will be well down at that frequency.

[pdf64]

…
When Fender switch to Schumacher made OTs the interleaving went by by!

My understanding is that the 125A6A / 125A7A / 022848 OT used in the black and silver panel Bandmaster, Pro, Tremolux, Vibrolux (and reverb versions, as applicable) with 2 hole fixing were not interleaved.
But the other larger OTs used in the 6L6GC amps, ie with 4 fixings, eg Super Reverb, Twin Reverb, were interleaved.
Here’s pics of a drip edge SR OT showing the secondary section connection wires -



It looks to me like the secondary has 3 sections, the primary has 5 sections.
Note the wood shim / block along the centre of the laminations, presumably used to give a smoother radius to the corners and so reduce stress on the initial windings.

[Phil_S]

Sorry for taking a minor diversion on the wood block. Several years ago, I had an old blown transformer and decided I'd unwind it just because I could. (It took forever to split each lamination layer so they could be removed.) I was wanted to see how it was made. It had a wood block like that. It's an interesting thought that it might provide some relief for the inner windings. My reaction on the wood block was that it was probably inserted to take up the slack between the bobbin and the lams, basically to stabilized the placement of the core. I don't know, really, I don't. Just a thought...

[pdf64]

…
When Fender switch to Schumacher made OTs the interleaving went by by!

My understanding is that the 125A6A / 125A7A / 022848 OT used in the black and silver panel Bandmaster, Pro, Tremolux, Vibrolux (and reverb versions, as applicable) with 2 hole fixing were not interleaved.
But the other larger OTs used in the 6L6GC amps, ie with 4 fixings, eg Super Reverb, Twin Reverb, were interleaved.
...

I got the above info from the Mark Baier article 'Where It All Began - Essential Ingredients of the Tweed Tone', p142-143 of the dreaded 'The Tube Amp Book' 2003 edition. Here's the relevant section -