Considering building this, maybe UL

[Joe6v6]

This is a layout I made several years ago , Cathode bias TW Express with EL84's. I plan on using an 18watt Power Transformer 290-0-290 120ma but with 5v rectifier taps. & the output trans I have has ultra linear screen taps & I may want to utilize them.
Any glaring mistakes? Or suggested changes and if I use the UL taps can I get rid of that 40uf filter cap?


Any help or advice is appreciated - Joe

[sluckey]

That 80µF is too big for the GZ34. You can omit the 40µF screen node cap but I would leave it because it helps provide a cleaner B+ for the little tubes. It's also possible you wont like the U/L, so having the screen node cap makes it easy to change.

[Joe6v6]

Good , I think I will change that 80uf cap to 40 & build it the way its drawn & can always try UL mode afterwards.

[pdf64]

A schematic is helpful, I find wading through layouts rather off putting.
Why fit standby and mess with the wonderful slow, smooth ramp up of the HT voltage that a GZ34 provides, which serves to eliminate voltage and current surges there?
If you must have standby, why use a hot switching type, that slams ‘off the scale’ surge current through the GZ34 plates every time it’s flipped into operating mode?
I can’t recall any UL amp with a decent rep that doesn’t feed the OT via a CLC pi filter. If that is omitted then a large ripple signal is fed to the g2s which, being a grid, amplify it such that it modulates plates current. Thereby creating an amp that exhibits weird ghosting at high outputs, as the HT both modulates the signal output, and causes ‘sum and difference’ artefact distortion.

[shooter]

I used UL with CRC, but I use SS rec and verify low ripple, typically tap the OT from the 2nd tap

[Joe6v6]

Why fit standby and mess with the wonderful slow, smooth ramp up of the HT voltage that a GZ34 provides

Good point , ive heard that before & if I use the GZ34 rectifier I will eliminate the standby, also like I said I put this together sometime ago just following the TW express schematic & changing things as I went. I never made a proper schematic. 

[Bieworm]

What is the attraction to UL nowadays? I'm not a connaisseur ,but back in the 90's I had a 1976 twin reverb that sounded sooooo much less nice than the 1966BF twin a friend owned. I recall the UL fact ruined a lot of the sonic experience... don't know if that's true, but it was the word back then

[shooter]

the UL fact ruined a lot of the sonic experience...

some big amp Marshall players might disagree 
I've found UL helps "tame" the nasties you can get overdriving xSE amps, Only built 1 in PP, the amp found an owner that thought it was the "magic sauce".  It's basically the half way house between pentode and triode.
The OT's don't cost much more with a UL tap so it's an easy test

[Joe6v6]

What is the attraction to UL nowadays?

I only wanted to try it in this amp because the out put trans I have has the taps. Ive read that UL got most of the blame for silverface amps when other changes were more to blame.  The route 66 amps Ive built that use it turned out very nice.

[pdf64]

What is the attraction to UL nowadays? I'm not a connaisseur ,but back in the 90's I had a 1976 twin reverb that sounded sooooo much less nice than the 1966BF twin a friend owned. I recall the UL fact ruined a lot of the sonic experience... don't know if that's true, but it was the word back then

For any rig, the speaker used is its ‘voice’, even a great amp through a mediocre cab can’t sound any better than ‘ok I guess’.
So, did you try plugging your TR into his cab? Or his TR into your cab?
If not, then 90% of the difference you recall may well have been due to the cabs, principally the mediocre speakers used in those high power late 70s range amps, at the base models, factory upgrades were available.
And they weren’t even UL, not in the usual sense anyway; the primary taps are at about 12.5%, rather than the typical UL 40%. The power stage operates in regular pentode mode, near as dammit, the taps were perhaps mainly just to take some stress off the screen grids. Which was necessary due to the higher HT and hence power output of this range. 

What is the attraction to UL nowadays?

I only wanted to try it in this amp because the out put trans I have has the taps. Ive read that UL got most of the blame for silverface amps when other changes were more to blame.  The route 66 amps Ive built that use it turned out very nice.

Haha, that’s about the only UL amp with a good rep that doesn’t have a pi filter HT.
What spec OT did you use, ie primary impedance?

[Bieworm]

What is the attraction to UL nowadays? I'm not a connaisseur ,but back in the 90's I had a 1976 twin reverb that sounded sooooo much less nice than the 1966BF twin a friend owned. I recall the UL fact ruined a lot of the sonic experience... don't know if that's true, but it was the word back then

For any rig, the speaker used is its ‘voice’, even a great amp through a mediocre cab can’t sound any better than ‘ok I guess’.
So, did you try plugging your TR into his cab? Or his TR into your cab?
If not, then 90% of the difference you recall may well have been due to the cabs, principally the mediocre speakers used in those high power late 70s range amps, at the base models, factory upgrades were available.
And they weren’t even UL, not in the usual sense anyway; the primary taps are at about 12.5%, rather than the typical UL 40%. The power stage operates in regular pentode mode, near as dammit, the taps were perhaps mainly just to take some stress off the screen grids. Which was necessary due to the higher HT and hence power output of this range. 

What is the attraction to UL nowadays?

I only wanted to try it in this amp because the out put trans I have has the taps. Ive read that UL got most of the blame for silverface amps when other changes were more to blame.  The route 66 amps Ive built that use it turned out very nice.

Haha, that’s about the only UL amp with a good rep that doesn’t have a pi filter HT.
What spec OT did you use, ie primary impedance?

Disagree... the 1976 had the JBL D130' s in it. Those are plenty to talk about, but mediocre is not the word I'd use.
Those SF twins, or BF for that matter are loud amps, but they don't seem to cut through the mix well. The CVR I had at that time was way more pronounced. Soundwise I'd choose the CVR over any twin all day long. In fact  the fellow guitarist in my band has been playing his 67 twin for years and has been begging me to sell my CVR to him for years too. I ended up selling my CVR after I modded my VK to bias vary trem and the lux was obsolete...

[thetragichero]

I've heard part of the issue with those was using global negative feedback (or how it was implemented at least)

[Bieworm]

I've heard part of the issue with those was using global negative feedback (or how it was implemented at least)

The CVR? No issues.. just sacrifice silence for good tone. It hisses, yeah.. so what? Only mod it needed was the reverb upper medicine. I added the neg feedback loop by switch. It was never on.. the amp turned from naughty to nice... I like naughty.
Maybe if it was rebuilt with some quality components it would have been quieter, but it didn't bother me as a gigging amp. The trem was to die for. So I copied that kinda in my VK...

[2deaf]

Disagree... the 1976 had the JBL D130' s in it. Those are plenty to talk about, but mediocre is not the word I'd use.
Those SF twins, or BF for that matter are loud amps, but they don't seem to cut through the mix well.

Minor point, but Fender didn't start making 135W Twins until part way through 1977.

I once put JBL K120's into a 100W TR and it cut through the mix really well.  In fact, people would blink their eyes and step back when I turned that thing up.

[2deaf]

If you don't use tube rectification, just capacitance with SS rectification works fine.  Brute force capacitance, that is, like this:


 

[Willabe]

What's a 'CVR' and a 'VK'? 

[Bieworm]

What's a 'CVR' and a 'VK'?

CVR = custom vibrolux reverb
VK = vibro king

[thetragichero]

i didn't know those abbreviations either. i was mainly speaking of 135w bassmen/twins

[2deaf]

i was mainly speaking of 135w bassmen/twins

That's what I thought you were speaking of along with the Quad Reverb 135, PA 135, Dual Showman Reverb 135, Super Six Reverb 135, and the Vibrosonic Reverb 135.

[thetragichero]

I've got a '78 pa 135 on my bench I'm working on and off to convert for guitar (made my own eyelet board and it'll be anything but fenderish). these are dirt cheap and i couldn't buy the iron for what this went for

[pdf64]

What is the attraction to UL nowadays? I'm not a connaisseur ,but back in the 90's I had a 1976 twin reverb that sounded sooooo much less nice than the 1966BF twin a friend owned. I recall the UL fact ruined a lot of the sonic experience... don't know if that's true, but it was the word back then

...So, did you try plugging your TR into his cab? Or his TR into your cab?...
...principally the mediocre speakers used in those high power late 70s range amps, at the base models, factory upgrades were available...

Disagree...

Are we to assume that you didn't try that then?

... the 1976 had the JBL D130' s in it. Those are plenty to talk about, but mediocre is not the word I'd use...

Agree, hence my description of the base speakers being mediocre but factory upgrades being available.
So, was your TR with the JBLs a 1976 100W, or the later 135W model?

Also regarding BF to SF like model comparisons, people seem to think that like settings should result in a like response. That's incorrect, some of the control tapers, eg for mid and bass, tended to be different. And what do they do with the SF's master vol control? People seem to think they should turn it down eg halfway, rather than up full, to make it equivalent to a BF. Again incorrect, and to compound the variance, with some models, that can bring in a bright cap into play.

[Bieworm]

What is the attraction to UL nowadays? I'm not a connaisseur ,but back in the 90's I had a 1976 twin reverb that sounded sooooo much less nice than the 1966BF twin a friend owned. I recall the UL fact ruined a lot of the sonic experience... don't know if that's true, but it was the word back then

...So, did you try plugging your TR into his cab? Or his TR into your cab?...
...principally the mediocre speakers used in those high power late 70s range amps, at the base models, factory upgrades were available...

Disagree...

Are we to assume that you didn't try that then?

... the 1976 had the JBL D130' s in it. Those are plenty to talk about, but mediocre is not the word I'd use...

Agree, hence my description of the base speakers being mediocre but factory upgrades being available.
So, was your TR with the JBLs a 1976 100W, or the later 135W model?

Also regarding BF to SF like model comparisons, people seem to think that like settings should result in a like response. That's incorrect, some of the control tapers, eg for mid and bass, tended to be different. And what do they do with the SF's master vol control? People seem to think they should turn it down eg halfway, rather than up full, to make it equivalent to a BF. Again incorrect, and to compound the variance, with some models, that can bring in a bright cap into play.

It was a 100W with MV,  sorry.
But I must say I've had 2 SF twins and a 90s twin amp. Everytime I bought one I found it sounding great until I took it to practice. I found thrm always disapearing in the mix. Really bland in any setting... not my cup of tea. And for home use they aren't the best choice. I play mostly my Tremolo TMB reverb. It's a JMPGuitars design. 18 watt raunchy little amp with plenty volume. Lightweight... jimi in a box