Using a GZ34 in an 18 watt

[john1056]

I've read a couple of posts where people say they are using a GZ34 in their 18 watts. Does one have to do anything special to use a GZ34? My tranny (from GDS) has the 5 V secondary, so can I just wire it in (for example like it's wired in the 36 watt layout)?

Thanks!

[chickenpickin]

Yep, use the 5V taps and you should be good to go. The GZ34 does pull more filament current than a 6CA4 so your power transformer will run a bit hotter. But the GDS tranny is rated at 2A on the 5V tap which is about what the GZ34 pulls. The one thing to watch out for is increased plate dissipation on the EL84's. Since the GZ34 has a lower effective supply impedance than the 6CA4, your plate voltages will rise. Be prepared to increase the cathode resistor value until the plate dissipation is within an acceptable range. Good luck!

Mick

[T-bones]

What would be the point of using a more exspensive rectifier tube in that circuit. They can be three to four times the price of a 6CA4. Neither tube is a tone factor. They do there AC-DC thing and thats it. I must say some people really have huge imaginations when it comes to GZ34's and such. I'd say save your money and stay with the original design. T-bones.

[myker]

to me the gz34 barely has any sag, so you might as well use diodes.
mike

[novemberrain]

A GZ34 will indeed sag... if you hang a couple hungry EL34s off it and crank 'em up.

Within the current demand of a pair of EL84s... it won't sag. Not enough to mention, anyway.

[HeeBGB]

to me the gz34 barely has any sag, so you might as well use diodes.
mike

Ditto

[markd]

Does one have to do anything special to use a GZ34? My tranny (from GDS) has the 5 V secondary, so can I just wire it in (for example like it's wired in the 36 watt layout)?

As mentioned you will need to consider dissipation because the plate voltages will rise significantly using a GZ34. An increase in Vp will alter the tone of an amp no matter what type of tube or rectification you use. So using a GZ34 will change the tone of your amp. Maybe for the better, but that will be up to your ears.

The vintage Marshall 20watt uses the same PT voltages as an 18watt(300-0-300 sec.) with SS rectification. The plate voltage on mine is around 400v. And it has a 125 ohm cathode resistor. Marshall didn't seem too concerned about dissipation. Does anyone know if the 20watt reissue uses a 125 ohm cathode resistor?
Anyway this increase in Vp is one reason the 20watts sound so different than the 18's. If you have heard them both that might give you some idea of what to expect.

The 36watt layout is a good guide for hooking up a 5v octal rectifier tube. If you put in an octal tube socket for the rectifier, you can also use a 5V4 for lower plate voltage. Or even a 5Y3, or 5Y4, for even lower Vp. Using an octal rectifier socket is more flexible than a 9 pin socket, in that way.
markd

[john1056]

Thanks for all the advise and opinions. I ordered the GZ34 by accident, so I'll just send it back and order the stock tube.

[PhatTele]

MarkD - I was looking at the Weber copper cap spec page (http://www.webervst.com/ccap.html) ...Generally speaking, would the 5V4 be a good octal equivalent to the EZ81 9-pin rectifier? PS - I'm basing this question soley on the CC specs for both rectifiers (which look pretty close to one another).

[markd]

MarkD - I was looking at the Weber copper cap spec page (http://www.webervst.com/ccap.html) ...Generally speaking, would the 5V4 be a good octal equivalent to the EZ81 9-pin rectifier? PS - I'm basing this question soley on the CC specs for both rectifiers (which look pretty close to one another).

The 5V4 is a bit stiffer than the EZ81. So a bit higher plate voltage. But not too much. The 5Y3/5Y4 would be a bit less stiff than an EZ81. Either could sound good. I really like a 5V4 in a Deluxe Reverb but have never used one in an 18watt. If you are having a CC made, they can match the EZ81 specs on an octal base I'm sure.

[john1056]

I noticed Tube Depot has Philips 6C4WAs on the cheap, will these work in place of a 6C4A?

[PhatTele]

MarkD - Thanks for that info. I've got two 18Watters under construction as we speak (one combo and one head). I'm thinking that I might try the 5V4 in at least one of them. That kind of tight for this type of amp may not necessarily be a bad thing.

[phsyconoodler]

I just finished an 18watt trem head and used a 275-0-275 PT with a GZ34 rectifier. It has 356.5 volts at the plates.This amp is absolutely sweet in every way.It has sweet cleans and bone rending crunch tones,exactly like Jimmy Page's early live stuff.It is truly remarkable how good it sounds.The plates aren't glowing so they can't be biased too hot.We'll see how they last.It does not sound anything like the 20watt reissue I tried at my local guitar shop.It flat out kicks it's ass in every way.I also played a Budda 18watter there and it was kind of lame sounding compared to mine.I'm not claiming to have the best head on the planet,I just came up with a killer PT & OT combo.I have heard the sounds in the Zounds section and mine sound every bit as good.when you get 'that tone' you can't stop playing.You all know what I'm talklng about.I had it hooked up to a vox closed back cab loaded with two 90 watt mesa black shadows.This cabinet is killer all the way.The head sounds just as nice through a celestion vintage 30 and a little brighter with a G12H-50.I lucked out on the choice of transformers,as I was looking at voltages and availability of parts locally when I chose these ones.
Phsyco

[EBE]

I have used about 4 of the 5V4s in different builds now. Very similiar to the 6CA4 in my opinion.

[tkroeger]

Just curious about your choice of iron?

T