SS vs GZ34 rect but, only when clean

[pjd3]

Hello,

This is not so much a general question on "SS vs tube rectification" but, what may be found in a specific circumstance.

I've started a stereo tube amp component and hardware collection but still pondering whether to go solid state or a GZ34 for rectification.

This amp will be for small to medium venues and will be miced to keep stage volume relatively low. It is largely a pedal platform but, its natural clean tone is important.

What I am wondering is that if two tube amps had the same B+ voltage and bias but, one was solid state and the other had a GZ34 and only set to fairly low volumes (never approaching an overdrive state), would you expect to either hear or feel a difference between the two? Of course, due to a larger internal resistance of the rect tube and resulting change in time constant, I would expect a sag or compression when really pushing the amp but, how would this play out using relaxed clean tone volumes?

The reason I am wondering is that if there was no or very little experienced difference, then some money, parts and layout could be minimized and simplified in using a solid state rectification. It would change the transformer specs a bit to suit the PS. I want to try the Musical Power Supplies transformers as I've been hearing OK things about them. But, after looking at the HT coil specs, it seems that I would need to choose between SS or GZ34 to keep 6V6 plates between say 430 and 460. I don't want to go as low as 400v, would like to keep the clean volume as stout as possible.

Hope I explained this right!
Thank you for your feedback. I've really never got to compare the difference in amps that close in power supply spec.
Best,

Phil D.

[pdf64]

The rectifier technology is only part of HT sag.
Valve rectifiers are intended to be used with a minimum degree of protecting resistance and with a maximum value of reservoir cap.

Whereas for solid state rectification, for our purposes, neither of those limits apply.
And FWB rectification with a single phase HT winding can be used.

It may be that much of what gets labelled valve rectifier sag is due to protecting resistance (possibly from transformer winding resistance) and lower values of reservoir cap.

So a solid state HT supply can be much stiffer than a valve rectified one, but it's not a given.

[R.G.]

Do what the solid state rectifiers intended to replace tube rectifiers do - stick in a power resistor approximating the conduction losses of a tube rectifier. The composite SS diodes and resistor get very close to the performance of a tube rectifier. This makes the question of SS vs tube rectifier largely moot.
Yes, some people will claim that they hear subtle variations in tone from SS-plus-resistor vs tube rectifier. I would sure like to see a clean test of that.

[TUBEDUDE]

To your question, playing low and clean, you will notice little difference.
As an aside, if you are running 6V6's over 400V, watch those G2 voltages. Are you looking at a Kelly style final?

[pjd3]

Thanks everyone for the usual high-quality feedback.

Kelly style final? Haven't of that one before. Is that when all the power tube plates explode at once?

To be a little more specific, I'm building what amounts to two Sluckey 20Watt Plexi's into one cabinet for a stereo amp. I just build a single one over the last year or so, and it has worked quite well for the genres of music and stage volume that my bands play at. I've just started a collection of what I consider great stereo time bases effects pedals, Stereo reverbs, Choruses, just received a Keeley Halo in the mail.

So, if I can get the level of tone and performance I've been getting but with utilizing the nice stereo field of these pedals, I'll be one happy camper. I get lots of compliments with just the single amp so, I expect to get even more once this is in place. Musical Power Supplies has a PT with 580-0-580vdc. With solid state rectification I would or should be seeing around a 405vdc B+ which would likely put about 400vdc on the plates of 6V6's. I'm using JJ 6V6's in the single amp 20W plexi and they are seeing about 435vdc. Sounds great, plenty of clean power at low to medium room stage volume and seem to be holding up great. It sounds as good (or better) than the day I put them in and the bias has not shifted a single milli amp.

But the single amp is a tube rectified. Should there not be much difference in the sound or feel of the amp, then I would be inclined to go solid state rect and save a few bucks and would open up the layout options a bit more. Having not directly experienced the difference between SS and tube rect, all else being the same, It would interesting to hear from those who had, and what they thought was different if any. My instincts said that there wouldn't be a significantly noticeable difference at low clean levels so, it doesn't surprise me to hear that they are not too different under those circumstance. I actually like have tube rectifiers just for the way they slowly come alive, instead of any stressful inrush current. Doesn't the HT coil see the 1st filter cap as sort of a short? But, I would strap a 47K resistor across the standby switch to make it a soft start trickle kind of thing instead of a "standby mute" switch. I did do an experiment and with 47K across the "standby switch" and there was about 35v after one second, 70v after 2 seconds, around 140v after 3 seconds across the main filter cap, so, that put a warm fuzzy in my heart for seeing a slower building of electrons in the filter caps. Seems to be worth a power resistor should inrush current be as aggressive as some have claimed. I would suspect the DCR of the HT coil helps with that somewhat but, I'm not certain how much.

Thanks again for your input. I'm thinking it may be fine going ahead with a SS rectifier without thinking I'm sacrificing any desirable element of the amps performance.

Best,
Phil D.

[TUBEDUDE]

Phil,
Sounds like a sweet little setup. This sounds like a good opportunity to compare tube vs. sand. I'm currently working on a Kelleyish project. Well, I'm stalled from recent tendon transfer surgery, so I have to live vicariously through the exploits of you and the other solder slingers here. Here's where I left off: