What Valves for my Dr Z Maz 18

ash96

Ok, Only had this a few weeks and I've managed to blow one of the power tubes in it!

Firstly, is there anything wrong with just replacing the broken one or should I redo them as a set?

Secondly, what are some good valves to replace them with?

digitalkettle

Should be a matched pair of EL84.

Misty

I have a Maz 38, and have replaced the power tubes several times with JJ EL84's from Hot Rox. I always ask for the distortion rating equivalent to Groove Tubes 6, as that is what Dr Z put in the amp in the first place. My understanding is that Groove Tubes were just selected JJ's anyway. It works for me, and I've had no issues at all with the JJ's, though Dr Z seems to be be using EH's now. Hot Rox are pretty good at selecting and I'd recommend them. Definitely get a matched pair though.

Here's the tube info from the Z website:

http://drzamps.com/tube_info.html

ash96

Cool, so either a matched pair of THESE or if I want EH ones then THESE

Will i need to bias the amp after? In all honesty, I've always taken my amps to someone else to revalve in the past.

digitalkettle

Either of those would be fine...I use JJs myself.

No need to rebias a MAZ (cathode biased)...yay!

ash96

Sweet so I literally just pull one out and chuck the new ones in? This seems frightfully easy!

ash96

THESE  are the same JJ's arent they? bit cheaper here!

digitalkettle

Yep, so long as it's a matched pair: plug and play

Make sure you've some replacement fuses (two types) squirrelled away too...I had an issue on a MAZ Sr once: fuses popped but valves were fine.

Cirrus

If I might recommend Karltone, good prices, quick postage, matches+burns in at sensible voltages and occasionally contributes here.

BowynMadley

I have 2 pairs of groove tubes platinum matched el84s that are brand new but not boxed. I no longer have an amp that runs them so I'll probably sell them if your interested?

Misty

ash96 said:

Cool, so either a matched pair of THESE or if I want EH ones then THESE

Will i need to bias the amp after? In all honesty, I've always taken my amps to someone else to revalve in the past.

I would buy whatever was in the amp originally. If it was Groove Tubes, JJ's will do just as well. If it was EH's then go for it. Groove Tubes were taken over by Fender some time ago, as I understand it, and apparently the quality control is not as good, though I'm happy to be corrected. Bear in mind that Dr Z is very fussy about what he puts in his amps, and he hasn't used GT's for some time. He also changed from JJ's to EH's because of quality issues, but all I can say is that I've had no issues at all buying JJ's from Hot Rox.

Digitalkettle is totally correct, no biasing, just remove the old tubes and put the new ones in. That's it.

Pete24v

I have a Maz38. I put TAD EL84's in there and the amp took one of them out straight away, then blew a fuse. I took the amp back to Hotrox where i bought the valves from, Mark suggested i put in some Groove Tubes. He put them in and let the amp run for a few hours, all was fine. Two gigs in and another fuse blows.. replace it and finish the gig. Next gig another fuse goes..

I then bought a standard set of JJ EL84's from Karltone, 1yr later (and no fuses!) they are still sounding great. I emailed Dr.Z during all of this and they said 'at the moment' they are using Electro Harmonix power valves, i have a set of them waiting to go in when the JJ's fail.

Pete

jpfamps

I've just revalved a Maz18 in our workshop.

I used JJ EL84s.

This amp not only has quite a high voltage for EL84s (around 380 VDC), but it also doesn't have any screen grid resistors. This is very hard on the valves.

Groove Tubes, as has been pointed out ad nauseam, don't manufacturer valves, they test and rebrand other manufacturers offerings (GT have some models that appear to be made exclusively for GT by the usual suspects, but not any EL84s). The country of origin is denoted by a letter after the valve code. R = Russia, S = Slovakia, and C = China.

Groove tubes sell 2 types on EL84: a Russian model and a Slovakian model. The S model is as far as I can see a JJ, and R model looks like an EH.

I don't see any advantage in buying JJ valves with GT silk screened on them, and several disadvantages. You are paying extra for the valves to be shipped to the US to be tested and rebranded and then shipped to the UK; furthermore valves can be (and are) damaged by rough handling in shipping, so it would be better to have the valves tested nearer the point of use.

When GT started there simply weren't many (maybe any) companies testing valves. Now there are, so I would buy you choice of valve from one of the several companies in the UK offering matched EL84s.

ash96

Yeah I went for a pair of matched JJ's and they work perfectly!

Thanks for the advice guys!