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Suggestion for push pull output transformer.

There are any number of YouTube videos that show transformer winding. To me, the winding part doesn't look all that hard (and yes, I know practice makes it look easier) but figuring out all the details that go into designing the windings/transformer to do a good job is the skill.
 
All these talk about the mystery of OPT, sectioning. This is very simple,

1) half the primary,
2) secondary
3) the other half of the primary.

The rest are just packing it up.

this run from 3Hz to over 170KHz, better than a lot of the commercial ones. This is only a guitar amp OPT.

So why Sowter worth $400 and Hammond only $100? Sure it's not snake oil like the $100 cap, "special" resistor stuffs? Particular some other exotic transformer that are $1200 a pair!!!!
 
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You do usually pay for what you get as you learned with the cheap kit amp as there are a lot more interleavings which is complicating & time consuming to do! OPT's define a regular tube amp except for the OTL type! There many tubes and PS & good design come into play.
 
You always pay for what you get (unless you stole it) but getting what you paid for is another matter. ;)

Don't mean that as a slam, just a bit of friendly ribbing.

Far as that cheap amp kit I know there were some suggestions to move the operating point. Not to derail this thread, but was that ever done...lower B+ quite a bit, I think, and up the current?
 
whoaru99 said:
You always pay for what you get (unless you stole it) but getting what you paid for is another matter. ;)

Don't mean that as a slam, just a bit of friendly ribbing.

Far as that cheap amp kit I know there were some suggestions to move the operating point. Not to derail this thread, but was that ever done...lower B+ quite a bit, I think, and up the current?
Click to expand...
This is my thread, I do not mind derail!!!! As long as you have good ideas, I am all ears, anything and everything goes!!!

I did raise both voltage and current. I already improved the sound a lot. The thing that made the most difference is splitting the input tube ( originally they parallel both sides together) using one as gain and the other half as cathode follower. Cathode follower can source grid current of the power tube to get a little more power. That made the biggest difference. The THD was literally lowered by HALF. ( from 10% to 4%). The sound started to come out a little bit.

I then got rid of the tube rectifier to make up on the sag caused by increasing the plate current from 50mA to 70mA. The result is the +B did go up about 10V with 70mA. That improve the distortion and sound again.

I might be pushing the tube beyond the dissipation limit, but who cares. Problem is I still did not get the result, not even close. Even my cheapest Acurus SS amp beat it by a mile......say 100 miles.

But that's the end of the road. I feel I pushed in all directions and hit the ceiling for the cheap amp. The sound improved quite a bit, BUT still a yawner.

To be fair, my speaker is only about 88dB sensitivity, it is known to be hard to drive even with SS amp, I had to do custom speaker cable to get the most out of the speaker. These are all going against SE amp that has limited power......and more importantly, no GNFB where the output impedance is very high ( very low damping factor). I think the speaker is walking all over the SE amp. That's the reason I decided to give up on the amp. I ain't going to change the speaker for the amp particularly I don't like horn tweeter, I ain't going to spend thousands to buy a pair of high efficiency speaker that belong to yesterdecades. ( not even yesteryear). Those that want to hang onto the Altec from the 50s, good for them, I don't want any part of it.
 
I am narrowing down the choice, I am leaning towards KT88 tubes with UL. Looks like the optimal primary is 4.3K to 4.5K. Dynakit A431, Triode A431S, Lundahl LL1679 are the main choice.

I like the EI core of the first two as it's easy to mount. Lundahl need the cover kit to mount.

I really want to find a 4K primary or even something like 3.8K. I have to do more research whether I can use 3.3K primary which Lundahl has available LL1620.

So what say you?
 
Alan0354 said:
I am narrowing down the choice, I am leaning towards KT88 tubes with UL. Looks like the optimal primary is 4.3K to 4.5K. Dynakit A431, Triode A431S, Lundahl LL1679 are the main choice.

I like the EI core of the first two as it's easy to mount. Lundahl need the cover kit to mount.

I really want to find a 4K primary or even something like 3.8K. I have to do more research whether I can use 3.3K primary which Lundahl has available LL1620.

So what say you?
Click to expand...

HI Alan,

If you go with a 4.3k primary, or a 4k primary, it isn't really going to make any difference, because nobody's speakers are exactly 8 ohms (or in your case, 4 ohms).

Lundahl is definitely a higher end transformer than the A431, but dynaco stuff works well too. I'm guessing here you settled on using KT-88 tubes? I strongly suggest to go to a local high end audio store (there's got to be lots in the bay area!) and listen to an audio research amp, or a reissue Mac 275, or something else using 6550 or KT88. Just check what you're getting into.

Best regards

Max
 
maxhifi said:
HI Alan,

If you go with a 4.3k primary, or a 4k primary, it isn't really going to make any difference, because nobody's speakers are exactly 8 ohms (or in your case, 4 ohms).

Lundahl is definitely a higher end transformer than the A431, but dynaco stuff works well too. I'm guessing here you settled on using KT-88 tubes? I strongly suggest to go to a local high end audio store (there's got to be lots in the bay area!) and listen to an audio research amp, or a reissue Mac 275, or something else using 6550 or KT88. Just check what you're getting into.

Best regards

Max
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Nothing is cast in stone, this is just the thinking for now. I am still looking at 6L6 or EL34. Only reason I pick TK88 is because the data sheet actually show UL at 425V. All the others including 6L6 only have limited information. I am still long ways off.

I am even thinking of buying the Edcor 3.4K primary at about $107 each to experiment.
 
Alan0354 said:
Nothing is cast in stone, this is just the thinking for now. I am still looking at 6L6 or EL34. Only reason I pick TK88 is because the data sheet actually show UL at 425V. All the others including 6L6 only have limited information. I am still long ways off.
Click to expand...

Ya know,I don't recall ever seeing a datasheet showing the 6L6 used in UL configuration. Come to think of it, the only place I recall ever seeing the 6L6 used in UL was in the 135 watt version of the Fender Twin Reverb.Awfully loud,virtually no breakup (at least not at bearable volume levels!) and way too ''hifi'' sounding for guitar use.IIrc,they ran the B+ at around 500v,and the screens through the UL taps and 470R resistors. Don't know how well that arrangement would work with ''modern'' 6L6's though:naughty:
 
I've heard KT77s and 6CA7s, beam tetrodes which are otherwise "equivalent" to EL34s, are better suited/designed with UL operation in mind-- moreso than EL34s. Beam tetrodes seem to have more durable screens, which might explain this difference... if it's even real.

UL operation does expose the screens to fairly high voltage and voltage spikes/transients, but it also limits power dissipation compared to running them at a constant high voltage. I think it's recommended for a lot for tubes like the KT88 because these are expected to be used at 500+ volts, and under these conditions UL might be the easiest way to protect the screens.

Whether the tubes with more UL applications listed on the datasheet actually sound better in that configuration... hard to say...
 
Those old datasheets has holes in them. Like a lot of them show Vg2=250V. What is that good for? Everyone use the +B voltage in penthode mode, nobody create a +250V just to power the screen!!!
 
Alan0354 said:
Those old datasheets has holes in them. Like a lot of them show Vg2=250V. What is that good for? Everyone use the +B voltage in penthode mode, nobody create a +250V just to power the screen!!!
Click to expand...

A lot of tubes were designed for use in radios. And actually putting the G2 voltage lower than the plate voltage and regulating it, can help performance. For example 6L6, 6550, or 807 with G2 about 300V. It is a cost saving measure to make it the same as the plate voltage, not an ideal condition.
 
maxhifi said:
A lot of tubes were designed for use in radios. And actually putting the G2 voltage lower than the plate voltage and regulating it, can help performance. For example 6L6, 6550, or 807 with G2 about 300V. It is a cost saving measure to make it the same as the plate voltage, not an ideal condition.
Click to expand...
Doesn't help us now. transistor datasheet usually are more complete.
 
You can usually determine a ratio between plate current and screen current, given some voltage relationship (i.e. roughly the same voltage), and use plate curves to guesstimate screen current. This isn't as useful under dynamic conditions (like UL) as we probably wish it could be, but it's not hopeless to try to stretch that info to other applications.

maxhifi said:
A lot of tubes were designed for use in radios. And actually putting the G2 voltage lower than the plate voltage and regulating it, can help performance. For example 6L6, 6550, or 807 with G2 about 300V. It is a cost saving measure to make it the same as the plate voltage, not an ideal condition.
Click to expand...

I'm not sure about performance but ironically this cost-saving measure is much harder on tubes than using a separate/lower screen supply! It's hard to adjust prices for inflation over time, but it seems like capacitors... and every other power supply part... are now cheaper, and tubes more expensive, than they were 50 years ago. Lower-voltage screens probably should have a place in a lot of new designs.

In terms of performance, big resistors are often used to protect screens at high voltages which will cause sag/compression. Not sure about the rest of the effects going on.
 
Alan0354 said:
Doesn't help us now. transistor datasheet usually are more complete.
Click to expand...

I hardly ever see full curves in transistor data sheets, though I admit I haven't looked at them that much. I think a company designing tube amps for profit should really buy a curve tracer, us hobby guys are at the mercy of data sheets though.
 
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