SE 5881 Trem-O-Nator connection point

[dwinstonwood]

Hi all,
But, I guess this question is aimed at sluckey...

Where is the best point in the signal path to connect the Trem-O-Nator?

Also, feedback is welcome from all! See any glaring mistakes? 

Thanks!

[sluckey]

My first choice would be to use a 250K INT pot and connect it to the top of your gain pot. Then remove that 220K that's parallel to the gain pot.

Is this already built? I would drop the 620Ω resistor and use a bigger choke. Then connect the OT and screen to node B. This will considerably reduce hum from that SE amp. Consider supplying the TON from unused node C.

[dwinstonwood]

Thanks sluckey!

No, it's not built... yet.

And, what do you know, I happen to have a hefty Hammond 159M, 15H - 100mA choke on hand that can handle both the plate and screen current.
https://www.hammfg.com/files/parts/pdf/159M.pdf

OK, I think I got your changes draw right. Thanks!

[sluckey]

That's how I would do it. As always, be prepared to experiment with the TON insertion point.

[dwinstonwood]

Thanks!

[dwinstonwood]

Here's a question about the SE OPT for this project. Is a 10W OPT too small for one 5881?

Hammond makes this one that's only $36.90 at Hawk:
https://www.hammfg.com/files/parts/pdf/1750B.pdf

If not, I guess I could just go with a single 6V6.

Also, this PT looks about right. It's "relatively" inexpensive at $88.10:
https://www.hammfg.com/files/parts/pdf/272DX.pdf

Thanks!

[PRR]

.

[dwinstonwood]

Thanks PRR. 11.3 watts in the third column. So, best to source a 15-20W OPT.

Those third column figures also indicate a 4,200 load resistance.

I might have to go to Edcor to find a 20W/4K2 SE. If I go that route, I might as well get the PT from them, too.

So that the end bells match. 

[DummyLoad]

Why the unreliable valve rectifier? You can simplify with SS and improve reliability significantly as well as increase the filter size for added PS noise reduction. The choke size depends on total system current load and desired ripple reduction. Why the valve recto? No sonic merits with SE.


--Pete

[dwinstonwood]

Thanks Pete, that's a really good point. There are also more PT choices by not needing the 5V/3A secondary - and, one less heater to wire up.
I'll go with SS diodes. 

[shooter]

So, best to source a 15-20W OPT.

just food of thought, or farm fodder


depending on means and end-game;
you might consider biting the bullet for Edcors SE 25W 4.xK pri 8ohm sec
you can use a 6V6 by doubling the speakers to 16ohm (2X12 comes to mind  )
you can run a KT88 when your 5881 seems lacking 
the options for experimentation will be there just nagging at the back of your mind IF you keep progressing down the lonely SE road 
the last 2 SE kt88's that went into the wild went idling at around 37W, 18-22W audio, the OT never got passed body temp, after guitarist pushed them for an hour, the OT just got a cozy warm feel 

[dwinstonwood]

Thanks shooter. That's all really good advice. I like the idea of going with the 25W Edcor to allow experimenting with other tubes. That's the better choice.

I sort of skimped on my SE stereo hifi amp, going with the Edcor 15W OPT's. It's running EL34's with a huge Edcor PT. It still sounds better than any stereo amp I've ever owned.

[shooter]

 
i've build a few tube and SS mono-blocks, the tubes win for sound and cool factor

[PRR]

Thanks PRR. 11.3 watts in the third column. So, best to source a 15-20W OPT....

What is this? Hi-Fi? Government work??

10 and 11 are "the same" for a stage amp.

The power rating for an audio transformer is not a Blow-Up number. It is where the THD at a specified frequency rises. Note that this case is 13% tube distortion, so a little distortion in the transformer is no big deal.

Long ago I did much work with a 12W-17W amp and a "15W" OT. Even cranked to the max, it was not about the transformer.

[dwinstonwood]

Thanks PRR. Though, as a moderator, you must know that some of us tend to "overthink" this amp stuff when posting.

But, here's a question. How did they arrive at a load resistance of 4,200 Ohms in the third column? There's clearly more to the calculation than 350^350/23, which is 5,326.

Or, maybe it's the load with the least 2nd order distortion? Though, the lowest THD is at 3,600.

Thanks!

[dwinstonwood]

PSDU2 test with a 275-0-275 PT, and a 50uF reservoir, 15H choke, 50uF cap Pi filter before the power tube.
V(C2) which will feed the plate and screen of the 5881 shows the ballpark voltage I'm looking for, and is very smooth.

[dwinstonwood]

Recent talk of Weber TX's here led me to check them out. They have an affordable 5K 25W SE OPT with 2,4,8, and 16 Ohm secondaries:
https://www.tedweber.com/wse25/

For the PT I'm looking at the Hammond 270EX:
https://www.hammfg.com/files/parts/pdf/270EX.pdf

When I start buying parts I'll start a new thread.

[thetragichero]

i used this when i built my 6l6g vibrochamp (solid state rectifier and the 90ma fender-style choke before the plate node), mainly because at the time amplified parts was selling em for like 16 bucks shipped on reverb: https://www.tubesandmore.com/products/transformer-output-8-w-single-ended
never had issues recording through it for hours, but i'm also budget-conscious (which is why i have threads asking about series-string output tubes and other such nonsense  )

[dwinstonwood]

Thanks thetragichero, that's good to know. I doubt I'll ever be diming this thing for an entire evening, anyway. And, it will be for my own home use.

I think I read somewhere that Keef records with an SE 6L6 Tweed Harvard.

Here's the latest schematic. "Spot the Errors" contest in effect, as always:

The 2.2K/22uF RC filter has a cutoff frequency of 3.29Hz, and the 4.7K/22uF is 1.54Hz. With the big 15H choke before the 5881 it should have low hum if my lead dress and parts layout are good.