Recommend Black Face Deluxe Reverb Kit

[TheTinMan]

I've been fighting to get lower voltages in a 5F2-A build with a Mojo PT. My guess is that their transformers are replicas and do what a vintage PT would do with 110 VAC coming out of the wall, only we've got 120-125 VAC. Still, 10-15% is within vintage specs IIRC. (My B+ started out 50 volts over the 305 spec )

Another guess is that Marsh can't sell a "Fender" logo with his kits. They probably can sell a "Fender" logo for your old Fender - you just have to order it.

Chip

[pila]

Mojo PTs seem to have too much HV. My first 5E3 PT was from them, and the HV was out of sight. I removed that one and used one from Doug Hoffman, which was in the ball-park on high voltage.

[MWJB]

"so I put in some NOS RCA 6V6 tubes and biased them to 18.6 mA and 22 mA - that's close enough for me. The plate voltage in this amp is a womping 460V, so I'm a little over 70% dissipation on the hotter tube." Have you tried biasing to 30mA per tube, the RCAs will take it, the massive screen voltage is potentially more angerous for the tubes than the plate current. The higher current may pull down your plate voltage to 425vdc (it usually does in BF Deluxes).

"Consequently, every voltage I measured was 10-15% higher than the schematic." No amps in real life match the Fender voltages on schems & layouts, 10-15% higher is absolutely normal.

[Diablo]

I went back inside the amp for a few finishing touches. I installed a 3 A/1000V diode (IN5408) on each of the power transformer secondary leads that connect to the anode plates (pins 6 and 4) of the rectifier socket. I did this to protect the amp in case of a shorted rectifier. Then I started testing some old rectifiers in the amp. The JJ GZ34 that came with the kit put out 460V to the plates at idle. A NOS RCA 5U4GB put out 432V. An old Silvertone 5U4G coke bottle put out 442V. An old JAN Sylvania 5U4G coke bottle put out 435V. The interesting thing was how much the plate voltage dropped under a load. With the volume cranked to 9 and a big guitar chord, I saw momentary readings on my meter around 310V. I was surprised there was this much voltage sag. I then decided to measure power tube watts under a load. Same conditions, vol 9 and a big chord.....each of the 6V6 tubes was momentarily pulling over 45mA....wow! I was again surprised there was this much current. Fortunately, the voltage sag under load reduces the tube watts to a reasonable level. The idle bias was retested and was the same as when I started (19.6 and 22 mA). I did find that the idle bias changed about 1-2mA with each of the different rectifier tubes. I left the Sylvania rectifier in place and buttoned the amp up. It looks like I don't have to worry about high plate voltage with this amp, as long as I stick with a 5U4G rectifier. Now to go work on my playing. I want to thank everyone on this forum for all the great information and help with the Deluxe Reverb. Without the internet, I never would have even entertained the thought about building this amp or fixing up my Ampeg.

[TheTinMan]

I'm really glad it's worked out well for you!

Are you certain that the PT can handle the higher heater current draw of the 5U4GB tube? IIRC it pulls almost 3 amps vs. only 2 amps for a 5AR4/GZ34.

Chip

[Diablo]

I'm really glad it's worked out well for you!

Are you certain that the PT can handle the higher heater current draw of the 5U4GB tube? IIRC it pulls almost 3 amps vs. only 2 amps for a 5AR4/GZ34.

Chip

No, I'm not certain, just keeping my fingers crossed. Bruce (Mission Amps) recommended it and others on the net claim it's not a problem for the Deluxe Reverb. It's my understanding (maybe not correct) that many Fenders from the mid 1960s came with the 5U4GB, and there was some confusion on the schematics about the specific rectifier choice.

[Bruce / Mission Amps]

No, I'm not certain, just keeping my fingers crossed. Bruce (Mission Amps) recommended it and others on the net claim it's not a problem for the Deluxe Reverb. It's my understanding (maybe not correct) that many Fenders from the mid 1960s came with the 5U4GB, and there was some confusion on the schematics about the specific rectifier choice.

For what it's worth... I think the Marsh kits are just MOJO amp kits and I've always been under the impression that the power tranny they copied "originally" was a silverface Deluxe Reverb PT... which used 5U4GB rectifiers.

http://www.mojomusicalsupply.com/ite...008&id=MOJO761

Note: I don't know if this is the PT supplied in your kit.

Regardless, IMHO no great sounding Deluxe reverb ever has more then 440vdc plate voltage and the best ones are around 420vdc or less for that sweet-juicy, black face tone.
What you need to do is increase your idle current to about 26ma-28ma.
The tubes will be hotter and your plate voltage will drop more but the amp should sound really good too.

[phylomatic]

You didn't happen to take pictures did you?

[Diablo]

For what it's worth... I think the Marsh kits are just MOJO amp kits and I've always been under the impression that the power tranny they copied "originally" was a silverface Deluxe Reverb PT... which used 5U4GB rectifiers.

http://www.mojomusicalsupply.com/ite...008&id=MOJO761

Note: I don't know if this is the PT supplied in your kit.

Regardless, IMHO no great sounding Deluxe reverb ever has more then 440vdc plate voltage and the best ones are around 420vdc or less for that sweet-juicy, black face tone.
What you need to do is increase your idle current to about 26ma-28ma.
The tubes will be hotter and your plate voltage will drop more but the amp should sound really good too.

Yes Bruce, you are correct. The Marsh is a Mojo kit. I don't know if they change any of the components or just include their own instructions. The power transformer is the MOJO761, same as above. I'll try cranking up the idle current and see how it sounds. Thanks for the advice.

[Diablo]

You didn't happen to take pictures did you?

Not yet. I'll shoot some and see if I can figure out how to post 'em. What are you interested in seeing?

[TheTinMan]

Not yet. I'll shoot some and see if I can figure out how to post 'em. What are you interested in seeing?

Inside the amp - power supply section, preamp section, tube sockets, control pots from the back, plus what the finished product looks like...

Photobucket.com is ok for posting a short slide show but there are other alternatives.

Chip

[Diablo]

OK, let's see if this link works to Photobucket.
30 images for y'all. Not the neatest I've seen, but what the heck....it works.

http://s268.photobucket.com/albums/j...luxe%20Reverb/

I also rebiased to 26-28mA as per Bruce's suggestion. The plate voltage dropped to 423V with the Sylvania 5U4G rectifier. I haven't had a chance to play a guitar through it at this bias.

[phylomatic]

Thanks for the pics.

I just wanted to see the finished product. Just out of interest I read the whole thread and it felt a bit anti-climatic without getting to see the finished product. Very interesting read and looks like you did a good job. I'm completely new to this so I don't know if that means a whole lot, but it seems like a lot of fun.

[Diablo]

No real serious changes at all except:
use five 22uF-500v TAD main B+ filter caps (I think they are actually SINO import caps, but excellent),
Use a real NOS 5U4GB rectifier tube.

Bruce, I have a question for you. I find the bass notes more than a little farty at higher volumes. I put in the stock 16 mfd filter caps that came with the kit. Do you think the 22mfd caps would make a good improvement? I was also thinking about trying a Weber SS rectifier (the no sag type) replacement - one of those copper caps to improve the bass. Do you think the amp would stand the higher voltage and would it improve the bass?

[Bruce / Mission Amps]

I always use two parallel 22uF@500v caps there myself.
I think most of the woofie tone in these is from the full frequency gain of the preamp tubes... (try 4.7uF caps across the cathode biasing resistors instead of 22uF to 25uF) and the little cap that drives the phase inverter (don't use more then .0022uF to .0047uF) .... plus the giant .1uF caps that drive the power tube grids. Those can be reduced to .047uF with very little loss of tone.
Another good trick is to reduce the gain and balance of the phase inverter 12AT7 stage a little by replacing the 27K tail resistor with a 33K to 47K and the 470 ohm biasing resistor with 820 to 1200 ohms... experiment.