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Rectifier question

RussB

low rent hobbyist
Messages
11,158
I just bought a Bugera BC30. An AC30 sort of amp with 2 channels, 4 EL-84's and a GZ34 rectifier.

Manual states that 2 5V4G/A rectifiers can be used in place of the GZ34 (5AR4) for more sag and squash. Does this make sense? Seems the 2 5V4G's would still put out a lot of current.

I could understand 1 5U4GB or 1 5V4G/A in place of the GZ34

Next, what is the difference between a 5V4G and a 5V4GA?

Thanks
 

RussB

low rent hobbyist
Messages
11,158
Let me simplify. Does 1 GZ34 aka 5AR4 put out more juju than 2 5V4G rectifier tubes?
 

Timbre Wolf

Hyperspatial Gravity Surfer
Platinum Supporting Member
Messages
10,178
Let me simplify. Does 1 GZ34 aka 5AR4 put out more juju than 2 5V4G rectifier tubes?
I use a single 5V4G in my AC30CC1, and get a small relative voltage drop. It seems to me that two 5V4G would easily out-supply one GZ34.

- Thom
 

RussB

low rent hobbyist
Messages
11,158
I use a single 5V4G in my AC30CC1, and get a small relative voltage drop. It seems to me that two 5V4G would easily out-supply one GZ34.

- Thom

That's how I see it as well. Also, if one can run TWO 5V4G's that would be 4 amps of total rectifier tube current draw, while one 5U4GB would draw only 3 amps...So it would seem that would be an option as well. I'm still waiting to hear back from Bugera to get their take
 

Timbre Wolf

Hyperspatial Gravity Surfer
Platinum Supporting Member
Messages
10,178
I took a quick peek at the Bugera site. If you're not already aware, I must warn you that your amp is designed for mind-blowing distortion, terrifying punch and breathtaking cleans. Personally, I'd rather spend about $650 less at my local dive bar and get in the face of the giant dude with no teeth if I'm in the mood for terrifying punch.

They mention explosive attack (more fun! hopefully not food-borne :barf) with the GZ34, or smooth and round response with two 5V4's. That points to the kind of voltage drop I've experienced with one 5V4G in my AC30CC. Oddly, their product brochure tells you to plug in a pair of 5U4's (not included) for a smoother, more buttery sound. I'm guessing it would be a great mistake to plug in two 5U4 rectifiers, and when you speak with a Bugera tech, you might urge them to re-visit their brochure.

Sound like you're in for quite a ride with that amp Russ!

- T
 

pdf64

Member
Messages
7,655
My guess is that 2 x 5V4 would put out a lower but stiffer VB+ than a GZ34.
Cathode bias (if that's what it's running?) tends to act to limit the max current demand.
 

oldhousescott

Gold Supporting Member
Messages
2,812
Looks to be more a Matchless DC-30 clone, except the EF86 channel is now a 12AX7. Two 5V4s or one 5AR4 is straight off the DC-30 schematic. If it will handle two 5V4s, then one 5U4 or one 5R4 should be fine, too, if you're looking for a lot of sag in the power supply. I don't think I'd try two 5U4s.
 

Blue Strat

Member
Messages
30,192
I use a single 5V4G in my AC30CC1, and get a small relative voltage drop. It seems to me that two 5V4G would easily out-supply one GZ34.

- Thom
I thought so too, but many Matchless DC30 owners have the same option and report greater sag with 2 5V4s. Problem is that people often hear differences buy mis-characterize them or "hear" what they're "supposed to hear" according to what they've read.
 

Blue Strat

Member
Messages
30,192
Looks to be more a Matchless DC-30 clone, except the EF86 channel is now a 12AX7. Two 5V4s or one 5AR4 is straight off the DC-30 schematic. If it will handle two 5V4s, then one 5U4 or one 5R4 should be fine, too, if you're looking for a lot of sag in the power supply. I don't think I'd try two 5U4s.
One 5R4 is what I'd try.
 

RussB

low rent hobbyist
Messages
11,158
I took a quick peek at the Bugera site. If you're not already aware, I must warn you that your amp is designed for mind-blowing distortion, terrifying punch and breathtaking cleans. Personally, I'd rather spend about $650 less at my local dive bar and get in the face of the giant dude with no teeth if I'm in the mood for terrifying punch.

They mention explosive attack (more fun! hopefully not food-borne :barf) with the GZ34, or smooth and round response with two 5V4's. That points to the kind of voltage drop I've experienced with one 5V4G in my AC30CC. Oddly, their product brochure tells you to plug in a pair of 5U4's (not included) for a smoother, more buttery sound. I'm guessing it would be a great mistake to plug in two 5U4 rectifiers, and when you speak with a Bugera tech, you might urge them to re-visit their brochure.

Sound like you're in for quite a ride with that amp Russ!

- T


P.T. Barnum's great grandson must write the brochure's for Bugera!

There is confusion regarding which recto's to use, 5U4G vs. 5V4G. The chassis is printed with 5V4G. With the Chinese 5AR4, I get just barely 3 volts at the heaters
 

RussB

low rent hobbyist
Messages
11,158
My guess is that 2 x 5V4 would put out a lower but stiffer VB+ than a GZ34.
Cathode bias (if that's what it's running?) tends to act to limit the max current demand.

Thanks for that info! :beer

Cathode biased with a 100 ohm 5w resistor per tube
 

RussB

low rent hobbyist
Messages
11,158
Looks to be more a Matchless DC-30 clone, except the EF86 channel is now a 12AX7. Two 5V4s or one 5AR4 is straight off the DC-30 schematic. If it will handle two 5V4s, then one 5U4 or one 5R4 should be fine, too, if you're looking for a lot of sag in the power supply. I don't think I'd try two 5U4s.

Matchless-like but different...and WAAAY cheaper! I will say it sounds pretty good, even with the stock speakers
 

RussB

low rent hobbyist
Messages
11,158
The amp was a return, and priced accordingly. I fired it up yesterday, and within 5 minutes 2 of the power tubes were red plating! I installed a quad of Russian 6p19p-ev's I had. I really like those tubes and biased them at 90%

I put 2 Tungsrams in the #1 channel, a GE in the #2 channel, and a Sylvania long plate PI. Those tubes made a very noticeable difference in tone and feel
 

pdf64

Member
Messages
7,655
Cathode biased with a 100 ohm 5w resistor per tube
Are you sure that isn't 100 ohms per pair of EL84?
As there would have to be something unusual for 100 ohms per EL84 to be sufficient, eg low voltage screen grid supply.
 

oldhousescott

Gold Supporting Member
Messages
2,812
Cathode biased with a 100 ohm 5w resistor per tube
Are you sure those aren't the screen grid resistors? I'd expect they'd copy the DC-30 and use 62/10w and 68/10w for the cathode resistors (tied to the half-power switch).

Regardless, it's a cool twist on a classic. I was sorely tempted when it was the MF SDOTD a while back.
 

RussB

low rent hobbyist
Messages
11,158
Are you sure that isn't 100 ohms per pair of EL84?
As there would have to be something unusual for 100 ohms per EL84 to be sufficient, eg low voltage screen grid supply.
Are you sure those aren't the screen grid resistors? I'd expect they'd copy the DC-30 and use 62/10w and 68/10w for the cathode resistors (tied to the half-power switch).

Regardless, it's a cool twist on a classic. I was sorely tempted when it was the MF SDOTD a while back.


Damn, I feel stupid! You are correct. I did not see the cathode resistors.

2 open-box amps there right now

http://www.musiciansfriend.com/ampl...2-hybrid-guitar-combo-amp?condition=used#used
 
Last edited:

RussB

low rent hobbyist
Messages
11,158
I just had another look in the chassis. I found no cathode resistors...that's because the amp has adjustable fixed bias! The light should've come on in my head right away, because the adjustment pot is external.
 

oldhousescott

Gold Supporting Member
Messages
2,812
Interesting! The sales lit made me think cathode biased with the "class A 30 watt" designation. That, and the fact it's so similar in other ways to the Matchless.
 

Diablo1

Member
Messages
620
Looks to be more a Matchless DC-30 clone, except the EF86 channel is now a 12AX7. Two 5V4s or one 5AR4 is straight off the DC-30 schematic. If it will handle two 5V4s, then one 5U4 or one 5R4 should be fine, too, if you're looking for a lot of sag in the power supply. I don't think I'd try two 5U4s.
This. I built a DC30 clone (Ceriatone) and tested the various rectifier options/suggestions. Single 5U4GB, single GZ34, and two 5V4s. I really don't hear a lot of difference, and there is very little B+ voltage difference at idle between the GZ34 and two 5V4s. I seem to recall they were within 5 volts. I left the 5V4s in the amp only because I have plenty of 'em, and they're fairly cheap compared to NOS GZ34.
 

Blue Strat

Member
Messages
30,192
This. I built a DC30 clone (Ceriatone) and tested the various rectifier options/suggestions. Single 5U4GB, single GZ34, and two 5V4s. I really don't hear a lot of difference, and there is very little B+ voltage difference at idle between the GZ34 and two 5V4s.
It would be interesting to see which setup sags more under moderate volume playing.
 




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