5r4 rectifier Super Reverb?..

strat84

Hi guys im after a bit more sag/compression from my Super Reverb at lower volumes and have read you can swap a 5u4gb out for a 5r4 and re-bias to acheive this.. Just wondered if someone could confirm this?? 

Also I have found a few different types on Ebay.. is there much difference between 5r4ga, 5r4gy, 5r4wgb etc... There is a Raytheon 5r4wgb that is reasonably priced, is this a good brand?

Cheers

camf

I'm wondering the exact same thing with a Super-Reverb based Gartone Stageman. I was going to take the amp out to @ICBM this week to check out possibilities. 

ICBM

It should be fine. There is a slight difference in that the 5R4 is only rated for 250mA vs. the 5U4GB's 275mA, but I don't think the Super Reverb draws as much as that. (Although I'd have to check.) All the other ratings are much higher than the 5U4 and the filament draw is lower, so there's no risk to the amp either. There isn't any important difference between the GY/GA and GB - the B's voltage ratings are even higher, but there's no guitar amp that operates at 900V so it doesn't matter!

@camf - I have found an old GE 5R4GA in my collection, we can try that. If @strat84 can wait a couple of days I'll let you know the result .

ESchap

As I understand it, you need to watch the level of filter caps you put 5R4's into ... the spec sheet states 4uF!   Though I've read of these being commonly and succesfuly substituted in tweeds for 5U4G's.   @ICBM, if your GE has any issues, I've got an unused 1952 RCA 5R4GY you'd be welcome to try.

ICBM

ESchap said:

As I understand it, you need to watch the level of filter caps you put 5R4's into ... the spec sheet states 4uF!   Though I've read of these being commonly and succesfuly substituted in tweeds for 5U4G's.

Damn, forgot to check that! I reckon it will be OK if the forward current rating is the same though, that's what limits the cap size... so I can't really see it being a problem in a 5U4 amp.

ESchap

Mostly from the knowledgeable types on the "Amp Garage" but the 5R4 will take heavier filtering if they are in good shape.  Apparently it shortens their serviceable life though.

strat84

ICBM;164860" said:

It should be fine. There is a slight difference in that the 5R4 is only rated for 250mA vs. the 5U4GB's 275mA, but I don't think the Super Reverb draws as much as that. (Although I'd have to check.) All the other ratings are much higher than the 5U4 and the filament draw is lower, so there's no risk to the amp either. There isn't any important difference between the GY/GA and GB - the B's voltage ratings are even higher, but there's no guitar amp that operates at 900V so it doesn't matter!

@camf - I have found an old GE 5R4GA in my collection, we can try that. If @strat84 can wait a couple of days I'll let you know the result .

Thanks for that!

Yeah im in no rush to buy one.. Would be great to see how it turns out..

Also been looking into 6l6wgb's but they have mixed reviews regarding if they are safe in a Super.. Im just after the tone I get when I turn it up to 8! Or something like!

ICBM

strat84 said:

Also been looking into 6l6wgb's but they have mixed reviews regarding if they are safe in a Super.. Im just after the tone I get when I turn it up to 8! Or something like!

If you want that at any less than the volume you get at 7, you need an attenuator .

Tweaking the supply voltages and the valve types really doesn't reduce the volume a lot - it's more about tone and feel.

camf is coming round later though, so I will know a bit more then...

strat84

Yeah I thought as much!!

I think some hotter pickups in my Strat would help.. They're the Fender 57/62 so quite low output

camf

Well after having spent some quality time with @ICBM yesterday his advice for my Gartone Stageman was don't change anything, maybe just get a better GZ34 to replace the Sovtek on that's in it. We also ruled out replacing the speaker with a Gold as it was pumping out around 60 watts. Having wrestled it along to rehearsal last night (it's a sturdy beast), it behaved impeccably, sounding absolutely sublime. 

It was a stupidly loud rehearsal with an original 60s AC30, a silverface Bassman and my pumped up Super Reverb all going at it. Our poor drummer didn't stand a chance and aside from the occasional yelp through the PA, the vocals were swamped. It should have been terrible. It was bliss. And in a shocking turn of events, my lowly DS-1 has been restored to my pedalboard and surprised me in a whole new role. Great night. 

Thanks again @ICBM.

strat84

Cheers @camf!

Im guessing you like the Stageman then?! I think im the former owner..Did you get this from Rhys?? I once had it through a pair of 60's Jensen C10s.. Beautiful sounding!...

ICBM

No problem @camf .

I did find out some useful stuff - the 5R4 dropped the static HT voltage by around 20V compared to the GZ34 - less than I was expecting - but reduced the maximum power further than I expected, from 60W down to only 42W, which implies that its sag at high current draw is much greater than at low, ie it has a very steep forward resistance curve. (Valve rectifiers are not linear like a resistor.)

Bearing in mind ESchap's warning I didn't use the standby switch when powering up when using the 5R4 - which gives it a chance to 'slow start' - but I did measure the surge current with the GZ34 in going from standby to on, and it was dead on 250mA which is the rating limit for a 5R4 and hence almost certainly would stress it, even if it worked OK.

So I would be careful. The voltage drop and sag is probably not significantly more than a 5U4, and there's more of a risk of blowing it. The only real advantage I can see is that it has a much lower filament current draw than the 5U4 (2A vs. 3A) which can often make the 5U4 unsuitable, or at least more risky.

I still like the 5V4 best, for the way it sounds - but that has an even lower current rating of 175mA, so again it's not going to be safe to try in amps with heavier filtering (or even just higher current draw).

Also remember to check the bias if you're doing anything like this, the 5R4 caused a slight crossover distortion to appear at full power - I didn't adjust the bias since it was just an experiment, but it would have been necessary for proper use, even with a 5U4 I expect.

strat84

Thanks for that @ICBM..Very helpful!

I think i'll stick with the 5u4!!

Would putting 6l6wgb be risky at all??

Cheers

57Deluxe

strat84 said: Yeah I thought as much!!

I think some hotter pickups in my Strat would help.. They're the Fender 57/62 so quite low output

yep - just change guitar to a higher output Humbucker, much easier. The difference between my lower output Strat to my Les Paul through my SR is vast when it comes to achieving that blue-edged natural Deluxe drive...