NOS ANOS GZ34 Crazy Prices

[Blackburn]

Add some resistors for the proper voltage sag

GZ34 don't seem to sag in a linear manner. Not to say they can't be modeled, rather that it's not trivial.
Pete

I think they are the best rectumfriers ever. Don't know what you mean by non linear.

[Diablo1]

Add some resistors for the proper voltage sag

GZ34 don't seem to sag in a linear manner. Not to say they can't be modeled, rather that it's not trivial.
Pete

I think they are the best rectumfriers ever. Don't know what you mean by non linear.

He means the voltage dropped across the rectfier is not a linear function of the current. Resistors are linear. However, a GZ34 voltge drop curves are available. I just don't think it's all that important to sweat about 5-10 volts variance on the B+, depending on what type of rectifier you have in there. If you look at the GZ34 amp/voltage curves, they look fairly linear from 100-250 mA.
http://tubedata.tubes.se/sheets/035/5/5AR4.pdf

[Blackburn]

Oh. More knowledgable minds than mine at work here.

[Cygnus X1]

Turtles!



Actually, this dummy here ordered a Shunguang 5AR4/GZ34 for the 67 Deluxe Reverb.
I hope it doesn't blow anything up.

[Diablo1]

A little more background info on rectifiers. If you follow Fender's design progression from the 1950s to 1960s, you can see that the goal was to minimize voltage drop across the rectifier. That voltage drop is just wasted heat that doesn't contribute to the output sound volume. It also means you need a larger power transformer to supply the voltage drop. Fender progressed to using two 5U4GB rectifiers in parallel in the tweed twin 5E8A to handle high current with minimal voltage drop. The only trouble there is it requires 6 amps of heater filament current to supply those 2 rectifiers, more wasted energy. When the GZ34 became available, Fender dropped the idea of two 5U4GBs. The GZ34 handles 250 mA of current with a 10 volt drop, and it only needs 2A of filament current. The final progression was the move to solid state diodes which drop less than 1 volt and don't require any filament current. They also only cost around a penny. The only sonic difference you will get with the progression to solid state diodes is the elimination of voltage sag on the B+. A push-pull AB1 output stage draws a lot more current at high volume when you slam chords etc., so your rectifier type can influence the amount of voltage sag or drop, and can give a spongier attack. If your amp is a single eneded class A, then the current doesn't increase at high volume, and you don't get any additional voltage sag, so it's not influenced by the type of rectifier. Weber's Copper Cap rectifier is a tube rectifier simulator, with a few diodes and large power resistors to mimic the voltage drop of various types of tube rectifiers - GZ34, 5U4GB, 5Y3GT etc.

[Diablo1]

Turtles!



Actually, this dummy here ordered a Shunguang 5AR4/GZ34 for the 67 Deluxe Reverb.
I hope it doesn't blow anything up.

You can put a couple of diodes on the tube socket for safety in the chance that your tube shorts. That may save your PT from potential damage.

[pdf64]

Resistors are linear. However, a GZ34 voltge drop curves are available. I just don't think it's all that important to sweat about 5-10 volts variance on the B+, depending on what type of rectifier you have in there. If you look at the GZ34 amp/voltage curves, they look fairly linear from 100-250 mA.

I swapped the WZ34 copper cap for a GZ34 in one of my amps, and the cranked output rose from 50 watts to nearly 70; wasn't expecting that (as the static B+ was pretty close), it killed my favourite speaker (Weber 12F150 50 watt) in short order, which I been happily cranking for nearly 2 years.

The only sonic difference you will get with the progression to solid state diodes is the elimination of voltage sag on the B+

Just to quality that, no rectifier sag, most Si rectified B+ supplies will sag maybe 10% when cranked, due to copper etc transformer losses and increased ripple from draining the reservoir cap.

If your amp is a single eneded class A, then the current doesn't increase at high volume, and you don't get any additional voltage sag, so it's not influenced by the type of rectifier

That's the case with hifi, but most classic guitar amps are used overdriven, to some degree at least (my Marshall Superlead bright channel couldn't be played clean with a Les Paul etc); outside the linear range amp class doesn't really apply.
My experience is that class A amp's power supplies usually sag when overdriven.
Pete

[Diablo1]

.

I swapped the WZ34 copper cap for a GZ34 in one of my amps, and the cranked output rose from 50 watts to nearly 70; wasn't expecting that (as the static B+ was pretty close), it killed my favourite speaker (Weber 12F150 50 watt) in short order, which I been happily cranking for nearly 2 years.

Pete

I don't understand how the B+ voltage can be the same with the copper cap and yet you get 20 additional watts of output. Something funny going on there. Perhaps your GZ34 was acting up and not delivering it's rated 250mA of current?

[pdf64]

The real GZ34 maintains a higher B+ under heavy load than the WZ34.
So even though the static VB+ were closely similar, the cranked output of the amp is significantly higher with the GZ34.
Hence it's not trivial to model the GZ34, the voltage drop doesn't seem to be linear, one resistor (as per the WZ34) doesn't seem do it.
It may need an array of zeners and resistors.
The GZ34 in question is the old Brimar that came with my AC30 when I bought it 29 years ago!
Pete

[martin manning]

I don't understand how the B+ voltage can be the same with the copper cap and yet you get 20 additional watts of output. Something funny going on there. Perhaps your GZ34 was acting up and not delivering it's rated 250mA of current?

The average and peak current through the rectifier is higher at full power than it is at idle, maybe ~50% for a fixed bias amp. Matching B+ voltage at idle with a linear resistor means that the B+ at full power will be higher than for a vacuum rectifier due to the vacuum rectifier's non-linear behavior. This effect is exagerated by the fact that the peak current is 3-4X the average, and both the plate and screen voltages are affected.

[Diablo1]

I don't understand how the B+ voltage can be the same with the copper cap and yet you get 20 additional watts of output. Something funny going on there. Perhaps your GZ34 was acting up and not delivering it's rated 250mA of current?

The average and peak current through the rectifier is higher at full power than it is at idle, maybe ~50% for a fixed bias amp. Matching B+ voltage at idle with a linear resistor means that the B+ at full power will be higher than for a vacuum rectifier due to the vacuum rectifier's non-linear behavior. This effect is exagerated by the fact that the peak current is 3-4X the average, and both the plate and screen voltages are affected.

Yes, but PDF64 is saying that the GZ34 puts out 20 extra watts, with the same B+ at idle. That doesn't make sense. The link I posted for the GZ34 shows that the valve is very linear from 100mA to 250mA, which should cover the range of operation from idle to full boogie. Check out what the Valve Wizard has to say about this:
http://www.valvewizard.co.uk/fullwave.html

[pdf64]

Matching B+ voltage at idle with a linear resistor means that the B+ at full power will be higher than for a vacuum rectifier due to the vacuum rectifier's non-linear behavior

My finding was opposite to this, the GZ34 was non linear the 'other' way, ie lower than expected sag at high demand.
I was reminded of this post http://music-electronics-forum.com/t26515/#post229390 which indicates that mullard GZ34 were so good they should have been assigned a different designation.
Pete

[martin manning]

You are right, Pete, I had it the wrong way 'round. But, that would mean that you should get more power out of the vacuum rectifier than the silicon with a sag resistor. Here is a simulation that shows they are essentially equivalent, with the vacuum rectifier just getting the edge. This is a 2x EL34 fixed-bias push-pull stage, where I set the sag resistor to get B+ to match at idle, and then put signal in equal to Vbias. Vout is peak voltage into an 8-ohm load, about 29W. B+ max and min are the ripple peak and trough. Both plate and screen node filters are 22uF with a 4H choke in between... I'll have to try it again with a larger plate filter.

[martin manning]

Secpond pass with 47u reservoir... Not much different, vacuum rectifier still comes out a little ahead in B+ and output power at high power.

[Reeltarded]

Didn't we already have this conversation and everyone agreed that using tube rectifiers is a hapless expense?


(lmao)