6g4 Super Clone (mostly done)

[owen]

Edit 6/28/22: fired up and sounding good. couple small gremlins left. some intermittent static/white noise, and touch of tremolo motorboat.

Howdy all. I goofed when buying filter caps for my 6g4 Super clone. I got 500v rated F&T when the schematic calls for 600v. Would it be more prudent to do series filter caps say 300-350v each to handle higher voltage?

Or should I be looking at 20uf/600v caps with a good track record? Cursory search brings up Sprague Atoms for a boatload each (and I need 14 total min. for two brown amps) and, would they even fit the doghouse?

I’ll keep this thread going to document all my bonehead questions in one place.

[bmccowan]

I would use those F&Ts - I do not think you will go over 500v - If you do, frankly that is too high and you can cut it back by using a different rectifier or other approaches. I love those brown amps. I have built a brownface Princeton and a Deluxe (I swapped out the rectifier tube in this amp to lower the B+ a bit) and rebuilt a Concert. The tone is a real nice transition between tweed and blackface.

[owen]

I would use those F&Ts - I do not think you will go over 500v - If you do, frankly that is too high and you can cut it back by using a different rectifier or other approaches. I love those brown amps. I have built a brownface Princeton and a Deluxe (I swapped out the rectifier tube in this amp to lower the B+ a bit) and rebuilt a Concert. The tone is a real nice transition between tweed and blackface.

Thanks! I do hope my voltages aren’t that high when it’s complete. I was reading some complaints about higher voltage on power up, but then it calms down. If so, I’ll look at other fixes. I finished a brown princeton that is just amazing, so I’ve got two more brown panels started.

[pdf64]

If an indirectly heated GZ34 is used, and standby is eliminated, there will be no power up surge. Because the GZ34 is designed warm up slower than receiving valves.

However, beware of testing the amp with just the rectifier in place, as without the current draw of the other valves, the HT voltage will rise a fair bit.
A light bulb limiter is often sufficient to sufficient to reduce the voltage to a suitable level.

[owen]

If an indirectly heated GZ34 is used, and standby is eliminated, there will be no power up surge. Because the GZ34 is designed warm up slower than receiving valves.

However, beware of testing the amp with just the rectifier in place, as without the current draw of the other valves, the HT voltage will rise a fair bit.
A light bulb limiter is often sufficient to sufficient to reduce the voltage to a suitable level.

Noted. Thank you! I have a dim bulb i put together, as well as a variac.

[Esquirefreak]

I built a 6G4 clone some time ago and I use 600v caps on the first two nodes, but you'll be fine with 500v as long as you have the correct power tranny. Mine puts out around 425vdc on the plates @ 45mA. B+ roughly 430vdc. I'm using a Hammond 290DEX PT.

Also, If you're using a Hammond OT, swap the primary leads on the plates (versus the schematic), so the blue goes to where the brown goes and vice versa.

I can PM you the layout I've used with the changes I made, if you want me to?

/Max

[Esquirefreak]

Sorry, I (just now) got that you're not building a clone. Apologies!

/Max

[owen]

I built a 6G4 clone some time ago and I use 600v caps on the first two nodes, but you'll be fine with 500v as long as you have the correct power tranny. Mine puts out around 425vdc on the plates @ 45mA. B+ roughly 430vdc. I'm using a Hammond 290DEX PT.

Also, If you're using a Hammond OT, swap the primary leads on the plates (versus the schematic), so the blue goes to where the brown goes and vice versa.

I can PM you the layout I've used with the changes I made, if you want me to?

/Max

I’d appreciate your layout since info on these is scarce. I’ve got a mercury output transformer, but I wasn’t sure about their PT since they don’t publish any specs. I might go the hammond route then.

Had a hard time finding 600v caps that would fit the doghouse. Those spragues are gigantic. If the 500v are an issue I’ll mod it.

[sluckey]

I would buy four 70µF/350V caps and four 220K 2W resistors. Stack two caps with bleeders for the plate node, and stack two for the screen node. Use your 500V caps for everything else.

[Willabe]

I’ve got a mercury output transformer, but I wasn’t sure about their PT since they don’t publish any specs.

If you call Mercury Mag. and ask them for the specs for the PT you bought from them, they will tell you what they are.

[owen]

I would buy four 70µF/350V caps and four 220K 2W resistors. Stack two caps with bleeders for the plate node, and stack two for the screen node. Use your 500V caps for everything else.

thanks sluckey. i’ll swap those two nodes.

[pdf64]

F&T make 550V working / 600V surge caps. May be a special order for Jan http://www.die-wuestens.de/k1.htm

[Esquirefreak]

/Max

[owen]

/Max

thank you! can you explain some of your mods in the tremolo section compared to your older version B on your thread? Specifically the LED to what says VIT

just curious on your choices and what the end result is. i’m not savvy enough to pick it up by looking at it.

[Esquirefreak]

Vit is swedish for white, I forgot that didn't write in english on the layout 

I only had yellow, black and white hookup wire. I color coded the supply nodes based on the shrink tubing colors I had on hand at the time.

The LED biasing for the LFO is Sluckeys idea that I read somewhere on this forum. It makes for a bigger voltage swing and therefore a deeper trem. I also changed the plate load R to knock up the voltage some.

Did you get the filter board done? If you want to, I could post my version of it.

/Max

[thetragichero]

think of the LED like a theoretically perfect/infinite cathode bypass cap. since your lfo frequency is ridiculously low compared to the frequencies we are used to dealing with in guitar amps (like under 10hz low) this ensures you'll receive max gain for all oscillator frequencies. as a plus, you also get a cool led flashing in time with your lfo

[owen]

think of the LED like a theoretically perfect/infinite cathode bypass cap. since your lfo frequency is ridiculously low compared to the frequencies we are used to dealing with in guitar amps (like under 10hz low) this ensures you'll receive max gain for all oscillator frequencies. as a plus, you also get a cool led flashing in time with your lfo

that’s what i figured. slower trem with more intensity is always my goal. i’m curious how crazy the harmonic depth will get so i’ll definitely consider trying both.

my princeton is as slow as i could manage without losing it and it’s great, but the bias very trem is just particularly magical.

[owen]

Vit is swedish for white, I forgot that didn't write in english on the layout 

I only had yellow, black and white hookup wire. I color coded the supply nodes based on the shrink tubing colors I had on hand at the time.

The LED biasing for the LFO is Sluckeys idea that I read somewhere on this forum. It makes for a bigger voltage swing and therefore a deeper trem. I also changed the plate load R to knock up the voltage some.

Did you get the filter board done? If you want to, I could post my version of it.

/Max

i figured it was just colors like the others. i wired the filter board up a while back with 500v caps, but since then i’ve been considering sluckey’s idea of stacking 70/350 v caps, though may not be enough room under the cap pan.

i saw your thread with the two 30uf 600v caps, and have since considered going that route and using that same PT 290DEX for a bassman. funny enough I just figured that idea out a couple weeks ago when browsing their spec sheets.

[owen]

Finally putting this together: hammond 290DX (650), 2/4/8Ω OT, larger choke, modern tubes

I populated the board in 2020 when I started doing this, so I had to correct some of my bad technique and change some values. Thanks to sluckey for the filter pack suggestions, and Max again for his mods and data posted.

I kludged together a bias board out of parallel caps. should have it fired up tomorrow.

[Esquirefreak]

On a side note - You may want to try to skip the 1k5 grid stoppers on the 6L6 tubes, as per the original schema. I've tried both with and without and found that I preffered the rougher nature of not using grid stoppers there. Just a thought.

Really nice build either way and I think that the center volume amps are often overlooked.

Cheers!

/Max

[owen]

On a side note - You may want to try to skip the 1k5 grid stoppers on the 6L6 tubes, as per the original schema. I've tried both with and without and found that I preffered the rougher nature of not using grid stoppers there. Just a thought.

Really nice build either way and I think that the center volume amps are often overlooked.

Cheers!

/Max

I actually hesitated putting them in, but made sure it’s a quick de-solder. thanks for the tip.

[owen]

Okay! fired it up. everything works. heater supply is high (hammond PT, 6.8v on heaters) B+ and power tube plate voltage is a bit lower than the schematic at 445v per power tube using a 5ar4 at 123.2v from the wall (vs 460v on the schem). 495v with no tubes.

it is nice and loud at 70% on one 6L6 and 65ish% on the other (4mA difference)

aside from that; I have my first case of strong 120hz and a loud bit of scratch on the intensity pot along with heavy trem thump at full intensity.

I’ll do some tests this week and do a full voltage workup.

This amp is already everything I had hoped it could be, should be incredible once it’s fully healthy. AMAZING with a baritone telecaster.

enough power to run my 2x10 ceramic and 1x15 neo cabs at the same time.

[shooter]

120hz is most likely lead dress, large signal wires in close proximity to sensitive signal wires, too long wires for sensitive signals, bad/iffy PS caps....
scratchy is typically DC leaking into the signal path, (coupling, or TS caps getting damaged from heat) or poor solder connections or physical connections, like sockets.

[Keppy]

AMAZING with a baritone telecaster.

The wife and I tried so hard to irresponsibly purchase a bari over the weekend. Couldn't find one we liked.

[owen]

Tremolo section is driving me batty. 4 caps thud loud when lightly tapped with a chopstick, and all the wiring around the trem section is an antenna. moving wires doesn't make a difference in the base 120hz buzz level. With tremolo ON, V3 plate voltages once I put my meter on pin 1 or 6, the voltage is low at 90v and then increases as long as I have my meter probes on ground and that pin. With tremolo jack shorted, my voltages are as written on the attached layout.

Yesterday my wall voltage had the bias about 70%, today I'm on the colder side.

[shooter]

all the wiring around the trem section is an antenna.

look for cracked, loose solder connections. 

[sluckey]

That tremolo circuit is high impedance (lotta big resistors) and the modulator can be finicky. However, the oscillator/inverter should not act like an antenna. Look for bad ground. Double check your component values and look for wiring errors. Did you use a 10M INT pot? Did you follow the original Fender layout?

The revibe uses that same tremolo circuit. My schematic has some notes on it that may be helpful when troubleshooting and to just understand what's going on. Do you have a scope and/or can your meter measure the 5Hz oscillator sine wave?

     http://sluckeyamps.com/revibe/revibe.pdf

[owen]

That tremolo circuit is high impedance (lotta big resistors) and the modulator can be finicky. However, the oscillator/inverter should not act like an antenna. Look for bad ground. Double check your component values and look for wiring errors. Did you use a 10M INT pot? Did you follow the original Fender layout?

The revibe uses that same tremolo circuit. My schematic has some notes on it that may be helpful when troubleshooting and to just understand what's going on. Do you have a scope and/or can your meter measure the 5Hz oscillator sine wave?

     http://sluckeyamps.com/revibe/revibe.pdf

I used 10 meg pot, but they seem very poor quality (‘revisit’ branded), most of the issue comes from that intensity pot. I do have a scope, I’ll probe around tonight.

I did use the fender layout and schematic, thanks for the notes!

[owen]

edit:
after looking at sluckey’s revibe. replaced my mallory .01 low pass cap and moved one wire completely. 120hz was mostly gone. however, it has come back after just sitting idle for 15 minutes. it seems to get louder as my wall voltage fluctuates down to 121v, but when it settles back to 124, it goes away.

the 60hz still exists after cleaning up every joint. it’s about 5dB of 60hz when the amp is on vs ambient room.

so so close. bias is still in a great spot, just under 70%, 2.1 mA diff between tubes.

going to do the LED and speed mods and add a shielded panel to the top to see what happens.

The vibrato channel is VERY bright with a jazzmaster, so I’ll make the bright cap switchable, and treble cap back to 250pf (i tried max’s 100pf)

[owen]

rebuilt the filter board; added the trem LED, most of the buzz and hum is gone. there’s one final solder joint or component causing intermittent white noise.

once I solve that, this amp will be extremely quiet at idle.

bias vary trem is my favorite, but this harmonic tremolo is special.

curious what the 6g*-A tremolo circuit  sounds like with the extra triode.

[owen]

Swapped a red then a yellow LED for the bypass cap/resistor in the oscillator section per esquirefreak’s suggestion. Tremolo intensity is VERY weak compared to the 25:50/4k7 combo. even after changing the 4.7m to 470k, and the 100k plate resistor to 120k for kicks.

i’m repairing my scope this afternoon; so hopefully I can find intermittent white noise issue. hum is almost totally gone.

i’ve lifted all the caps and they seem fine.

the hunt continues.

[sluckey]

Swapped a red then a yellow LED for the bypass cap/resistor in the modulator section per esquirefreak’s suggestion.

His LED suggestion is for the oscillator, not the modulator.

[owen]

scope is back up. i’ve probed everything to the power tubes and the signal is stable, not noisy. the grids of the 6L6s at idle with volumes down have some movement. the plate voltage and bias current fluctuate a bit.

pulled negative feedback for these tests. i’ll try ordering another set of 6L6s.

His LED suggestion is for the oscillator, not the modulator.

mistyped, it was placed in the oscillation section in place of the 25-50 bypass cap and 4k7 resistor. the intensity was much deeper when the speed was 3/4 up, but weaker everywhere else on the speed pot, even dying out almost completely at “0”.

[shooter]

i’ve probed everything to the power tubes and the signal is stable, not noisy.

did you probe the speaker side of things?
bad solder/ loose ground might get white noise

[owen]

i’ve probed everything to the power tubes and the signal is stable, not noisy.

did you probe the speaker side of things?
bad solder/ loose ground might get white noise

yes, output too. clean sine til about 5 on each channel then it squares off into distortion by max output.

i’ve been checking every joint and lead with a magnifier and chopstick, reflowing a couple that looked funky, and changed for shielded cable on long runs.

worth the trouble, this amp is perfect for a 6g15 reverb unit.

[sluckey]

I'd like to see some hi-rez pics of the completed amp. I'm particularly interested to see the filter caps. Since there are six filter nodes it might be easy to get them jumbled up.

[owen]

I'd like to see some hi-rez pics of the completed amp. I'm particularly interested to see the filter caps. Since there are six filter nodes it might be easy to get them jumbled up.

here you go, close up of filter board, bias board, and the whole amp.

I DID mistakenly swap nodes 4 and 5 which led to wonky voltages but fixed that.

from left to right on filters:
white node 6 (v1 and 2) with its ground to preamp bus, blue node 3 to v5 plates, red node 2 after choke to v6 and 7 screens, white node 4, yellow node 5, black node 1

*Should ONLY node 6 ground to preamp and everything else to power ground?

[shooter]

i'm using this schematic as reference


out of both channels there's a .05/220k junction
set all the channels knobs to zero


clip your scope to the junction  DON't inject a signal or plug anything into the input jacks
bring each knob up slow and watch the noise level
do this to both channels


If you see something "lurking in the grass", see if you can tweak the scope to "pull it out"

[owen]

here are 3 higher res. tried with and without grid stoppers and it’s the same wrt noise, so they’re in for now

[owen]

thanks shooter. it’s a 6g4 but i’ll check there. also to note, just discovered the noise is there with the phase inverter pulled, wouldn’t that suggest the power section?

i'm using this schematic as reference


out of both channels there's a .05/220k junction
set all the channels knobs to zero


clip your scope to the junction  DON't inject a signal or plug anything into the input jacks
bring each knob up slow and watch the noise level
do this to both channels


If you see something "lurking in the grass", see if you can tweak the scope to "pull it out"

[Esquirefreak]

Here's how my cap board is grounded and I have had zero hum/buzzing issues with my 3 6G4-ish builds.

And yes, if the noise is there without the PI tube, the noise may be coming from either the power amp or DC supply.

[owen]

v7 6L6 is failing. now reporting 11mA less on its bias regardless of which socket it’s in. noise is much worse. the tube never red plated either. perhaps it’s just been that tube.

Here's how my cap board is grounded and I have had zero hum/buzzing issues with my 3 6G4-ish builds.

And yes, if the noise is there without the PI tube, the noise may be coming from either the power amp or DC supply.

that’s how I ultimately wired mine, screen also going to power ground everything else to preamp. thanks for that.

[shooter]

if the noise is there without the PI tube

missed that nugget 

[owen]

update: new 6L6s installed. did not correct the noise issue. bias is a bit cold with this pair but stable.

if the noise is there without the PI tube

missed that nugget 

shooter, I was wrong. noise IS there with PI in tact. I had pulled the wrong tube.

The problem noises (static fluctuations and some small pops) only disappear when removing v2 OR v4 modulator tubes.

With V2 pulled, static whooshing and pops gone. just carbon comp hiss and a little 120hz

with V2 reinstalled but V4 pulled, no static/pops, much less carbon comp hiss but same amount of 120hz.

so i’m still chasing 120hz, and these noises. have reflowed all joints and inspected all connections with magnifier, have swapped all tubes, have replaced many components.

I feel silly. the tremolux I just slapped together in a few hours was a walk in the park compared.

[owen]

OK. replaced a 100k carbon comp resistor to V2 plate pin 1. Replaced shielded coax from vibrato volume pot to the grid pin 2.

120hz is gone. Insignificant 60hz with chassis open to the room. The crackling that was present with both volume pots at zero is now gone, however when the volume is up on vibrato channel, there’s some of that intermittent static crackle.

it’s so much better. I’ll keep reworking the tremolo area and pay some mind to the pot.

Overall it’s quieter than the tremolux I built. I’ll see if I can’t massage a little more current out of these 6L6s, OR trade tubes to even both amps out a touch.

Bias resistance is at 27k (50k pot fully down) for -51v to the 6L6s. slightly concerning as schematic has a 56k resistor. bias caps are now 10uF 150v (8uf 150v on the schematic)

plate voltage and b+1 are at 455v, 35mA and 37mA picked off from the 1Ω resistors off 6L6s

[ac427v]

Long shot here. I once had contamination (flux or solder?) inside a pot that caused intermittent crackling. Took forever to track down. I found it when chopsticking the pot terminals. A new pot fixed it. Good luck!

[owen]

Long shot here. I once had contamination (flux or solder?) inside a pot that caused intermittent crackling. Took forever to track down. I found it when chopsticking the pot terminals. A new pot fixed it. Good luck!

that is very possible as deoxit didn’t help. this roll of kester has so much flux it drives me crazy.

ordered some new pots last night, had a few bad ones from CTS this year.