Yet ANOTHER Quick Question! Tube rectifier swap!

[tubedood]

Hi again fellow amp-tinkerers! I did a search around the interwebs this week to see if I could find some preliminary info on using a faster responding recto in a tweed Princeton circuit/build... it comes stock with a 5Y3 and I happen to have a few GZ34's and was wondering on the feasibility of using one in place of the 5Y3... thoughts are a jump in responsiveness/headroom towards the SS/diode feel but still a tube and maybe to allow a different output tube to be used (kinda like that Kendrick Roughneck). Would the best way to do this involve a different transformer/and or tap for the B+ or is it attainable thru other means? I haven't purchased anything in the power section yet so I figured lets ask the community their thoughts and see if this might be a decent idea! I will do my homework if someone can point me in the right direction!

Thanks again and have a great weekend,
Dale

[Justin Thomas]

My gut says <IF> your filter caps are up to snuff and able to handle about 40 extra volts, <AND> if you've got quality 6V6s in the amp, just plug & play. The 5Y3 & 5AR4 both draw 2A of heater current; the main difference as it applies to your amp is goin 6V6 to be the approximately 30-40V more B+ you'll get, because the 5Y3 drops around 50V & the 5AR4 about 20V.

Also, no reason a 6L6 couldn't be used with a 5Y3, since a Tweed Princeton is basically a Champ w. a Tone Control. If your PT 6V winding has the current, go for it.

Justin

[pdf64]

... info on using a faster responding recto in a tweed Princeton circuit/build... it comes stock with a 5Y3...

What is meant by 'faster responding'? It may indicate a misapprehension.

[Chuck H]

What is meant by 'faster responding'? It may indicate a misapprehension.

I've seen it as common nomenclature in pseudo "tube amp guy" circles. The idea (I think) is that the lower power supply resistance makes the amp respond faster on dynamics like attack.?. I can see where an overdriven amp may seem more articulate and less blurry on note separation with a lower power supply resistance with other circuit parameters allowed for. Making an amp seem like it's keeping up with the player.

[J M Fahey]

What is meant by 'faster responding'? It may indicate a misapprehension.

¨Painting with a very broad brush:

* power pentode gain depends on screen voltage, which tracks +V

* they act as *crude* compressors ... which is a large part of "tube sound" .

* when you pick a string, it starts with a strong attack

* in a stiff supply amp or an SS one, you hear it immediately, little or no gain variation respectively

* in a small capacitor (you can only use so much) lossy (tube rectifier) supply feeding power pentodes, specially if low or no feedback, first couple cycles (we are talking 1 or 2 milliseconds) will "turn compressor gain down" , which will recover a few milliseconds later , both "attack" and "release" time constants are very short here, you´ll hear guitar signal reappearing after that initial drop/dunk and to your ear it will "sound like" the pick attack arrived a couple milliseconds later and "as if it were swelled by a volume pedal" .

That "slow attack" is much used by some Blues Players who love that old but very expressive "greasy/smokey" Blues sound.
Notice that in their heyday they used Fender Tweed amps, of course because "that´s what was available".

Fender sound was in a constant evolution, from earliest "datasheet application" amps to Tweed to Blackface to Silverface.

"Small/mid" Blackface amps still used tube rectifiers and showed some of this sound, larger ones (Twin/Showman) already had beefy power supplies, more capacitance, **silicon diodes** and were stiffer but still "usable" ; Silverface started being "a little too stiff" so not much liked.

Sunn/Ampeg amps , won´t say were "disliked" , far fom it, but "not preferred" , way too "fast" if used with Guitar, and SS is the "ultimate Sin" as far as Guitar playing is concerned, ZERO "pick response".

[tubedood]

Hi all! Maybe not the best choice of words by my use of "Fast Responding"... I'm no fast style player (altho I was a child of the 80s and I still wanna be in a hair band hahaa). I did an amplifier build some time ago of a blackface Princeton with 2 6V6's and had it made in two ways.. One was with the 5U4 rectifier and another try was the same amp with heavier filtering and 4 IN4007 diodes. The 4007 one seemed to have more clean headroom and had a harder punching feel to it. Not sure of the physics involved but at the time the only things I was sure of were the voltages were higher on the SS and it seemed very efficient... That's where I was wondering if a rectifier such as the GZ34 would fit the bill as still a tube, yet provide the performance I guess is the term of the SS rectifier. I'm a novice totally and I am thrilled to have folks like you all to bounce ideas on! That was the purpose of the post, if I went with a GZ34, any hints to a power transformer that would have taps that would keep our voltages within reason?
Thanks to all of you... I have read your advice to others for years and I am excited to try a project. I apologize in advance if some of my questions are basic... I do try to research before asking!

Dale

[Chuck H]

How about some specifics then.?.

What is the plate voltage with the 5y3 tube?

What exactly do you want to change about the amps tone. Louder? Sharper attack? More and tighter bass?

How will the amp be used? Clean with pedals? Gritty with pedals? Would the pedals be dirt boxes adjusted for unity gain or set up for a boost at the amps input? Will you be cranking it up into overdrive much?

There are some things to consider WRT single ended amps in that a rectifier swap for more voltage/less power supply resistance doesn't affect things the same as with a push/pull circuit like your Princeton. So the change you propose may not give you much of what you want. If the voltage won't be too high with a 5ar4 there's no harm in trying it. And there may be other things that can be done to get you closer to your goal.

[Helmholtz]

¨Painting with a very broad brush:

* power pentode gain depends on screen voltage, which tracks +V

* they act as *crude* compressors ... which is a large part of "tube sound" .

* when you pick a string, it starts with a strong attack

* in a stiff supply amp or an SS one, you hear it immediately, little or no gain variation respectively

* in a small capacitor (you can only use so much) lossy (tube rectifier) supply feeding power pentodes, specially if low or no feedback, first couple cycles (we are talking 1 or 2 milliseconds) will "turn compressor gain down" , which will recover a few milliseconds later , both "attack" and "release" time constants are very short here, you´ll hear guitar signal reappearing after that initial drop/dunk and to your ear it will "sound like" the pick attack arrived a couple milliseconds later and "as if it were swelled by a volume pedal" .

That "slow attack" is much used by some Blues Players who love that old but very expressive "greasy/smokey" Blues sound.
Notice that in their heyday they used Fender Tweed amps, of course because "that´s what was available".

Fender sound was in a constant evolution, from earliest "datasheet application" amps to Tweed to Blackface to Silverface.

"Small/mid" Blackface amps still used tube rectifiers and showed some of this sound, larger ones (Twin/Showman) already had beefy power supplies, more capacitance, **silicon diodes** and were stiffer but still "usable" ; Silverface started being "a little too stiff" so not much liked.

Sunn/Ampeg amps , won´t say were "disliked" , far fom it, but "not preferred" , way too "fast" if used with Guitar, and SS is the "ultimate Sin" as far as Guitar playing is concerned, ZERO "pick response".

Yes, but screen compression requires a signal amplitude dependance of the B+/HT sag. It does not happen in pure class A (tube) amps.

[tubedood]

Hi Chuck I hope the weekends been treating you well! The amp pretty much is a simple project/practice amplifier. The idea started life as a Champ 5F1... but I wanted a little tonal control so I went with the 5FA-2 Princeton. After some research on simple mods that seem to fare well I am thinking of adding a switch to provide choices to the first gain stage cathode bypass cap (Thanks Enzo for the tip of adding a 1Meg resistor across the switch to avoid the POP noise), and possibly a switch or potentiometer for the feedback resistor. This is where the SS rectifier thoughts entered (increasing the clean headroom and punch)... which led to the possibility of the GZ34. If the amp ends up with a nice level of clean headroom it might be cool to have a simple effects loop (Ceriatone or Metro kit style) to let pedals be inserted. I was hoping to use as many old parts as possible, but haven't got any transformers yet till I am sure of the rectifier that will be used. Seems most 5F2-A's run roughly 190-210 on the preamp plates with a 5Y3 with 365-375 on the 6V6? If the GZ34 doesn't seem feasible I will stick with the 5Y3.

Lots of things to think over but I am having fun and learning!
Dale

[soundmasterg]

Yes, but screen compression requires a signal amplitude dependance of the B+/HT sag. It does not happen in pure class A (tube) amps.

Yeah but how many of those are really out there? Aside from single ended stuff, not much is really Class A.

Greg

[Helmholtz]

Yeah but how many of those are really out there? Aside from single ended stuff, not much is really Class A.

Greg

Well, this thread is about a Tweed Princeton design, isn't it?

[Chuck H]

The thing to know about single ended operation is that the tube will be idling at as much or more current than when it's conducting signal. What this means is that there's no power supply sag with increased signal conduction like there is with a push/pull amp. So the changes you propose won't affect this amp the same as it did your BF Princeton. With voltages significantly higher than 365/375 you would need to increase bias to idle the tube safely. This wouldn't make the amp any louder for clean tones because the bias point would be cold off center and the entire waveform is occuring in only the one tube between cutoff and saturation. It may make the amp a little louder when clipping, but the clipped wave form would be too asymmetrical. The asymmetry of single ended amps is said to give nice 2nd order harmonics. But if you get TOO asymmetrical it can sound ratty and harsh when clipping (like a silver face Champ ). So...

With no significant power supply sag for signal conduction power supply resistance becomes a moot point. So the only other consideration is voltage. Since you start stressing design limits at voltages which won't allow you to center bias the tube I wouldn't suggest increasing voltages either. And since the 5y3 is easily up to the job, less expensive than a 5ar4 and offers the desired voltages with transformers made for this design I would say don't change a thing. The clean headroom will be what it will be. The signal circuit could be tuned after the final incarnation of the amp is assembled, but the power supply is already close to ideal for this amp regardless of series resistance.

[loudthud]

On a GZ34, the cathode is connected to pin 8. This is where the filter cap should be connected. Sometimes a 5Y3 is wired with the DC output connected to pin 2 so when a GZ34 is installed, the 5VAC heater winding is connected in series with the DC. Will it make a noticeable difference? Try it and see.

[pdf64]

I think that in the context of a SE class A amp such as the Tweed Princeton, the 'speed' of the HT response is likely to be less significant to the amp's dynamic characteristics than would be the case with a p-p class AB (eg a BF Princeton).
Time constants of the grid and cathode circuits (especially at signal levels beyond overdrive) are likely to be the key factors; the HT is already 'fast'.
As Chuck H describes, changes that act to raise the HT voltage of a Tweed Princeton would seem to be a bad move.