Vol/Tone in a 5C5?

[RC99]

Hi All,

Dug up a very early amp build of mine...a Weber 5C5. Love this amp. Just trying to figure out how to voice each channel more similarly, since only one of them is connected to that 500pf cap so the other is always darker. Can the Vol/Tone mod, like the one that Mission sells for a 5E3, work similarly on a 5C5? Or can I basically just connect another cap and tone pot to the other volume?

[RC99]

I went ahead and tried it. It worked, but seemed to thin things out too much, so I went back to the original layout and trying different bright cap values on the 'normal' channel.

[Bruce / Mission Amps]

Yes, the Volume Mod Kit works on any of those "Fendery", two volume pots and a single pot for tone.

[RC99]

Thanks for replying, Bruce. Yeah, I just tried it (that I got from you!), and it did give it two independent channels, but I liked how the amp sounded before it, so switched it back. Might use it on something else, though.

Just ordered another 2x12 combo cab for it...I used the old one for another build. I love this circuit with the octal pres....some feel it's better for harmonica, but I really love it for guitar and I love the old Ampegs with them too. I'd really like to figure out how to make a legitimate 35-w version of it. Would it just be a transformer thing? Probably have to go fixed bias, too.

[Bruce / Mission Amps]

Thanks for replying, Bruce. Yeah, I just tried it (that I got from you!), and it did give it two independent channels, but I liked how the amp sounded before it, so switched it back. Might use it on something else, though.

Just ordered another 2x12 combo cab for it...I used the old one for another build. I love this circuit with the octal pres....some feel it's better for harmonica, but I really love it for guitar and I love the old Ampegs with them too. I'd really like to figure out how to make a legitimate 35-w version of it. Would it just be a transformer thing? Probably have to go fixed bias, too.

Yes, fixed bias power tubes is a must if you want more power.
No matter what anyone tells you... those amps will not make much more then about 20-24 watts in cathode bias.
Thinning it out is exactly what those amps need to have a more modern sound! ha ha.
That paraphase driver adds a certain distortion and "tone" that will limit the clean output power too.
The driver stage distorts before the power tubes....
The contact bias of the octal 6SC7 tubes limits the amp a bit too... and some think they are a little muddy.
You should try 6SC7GTs if you have the metal envelope ones... the glass ones sound better to me.
Drop the 100nF coupling caps to the volume pots to .033uf and change the 500pf treble bypass cap to around 680pF.
I prefer a 2K7-2W screen node resistor in those instead of the 10K.
And, if you go fixed bias, you need to block DC from the grid of the lower triode.... but you can use a GZ34/5AR4 rectifier and set the bias voltage so the power tubes idle around 30ma to 34ma each. That will kick it in the pants.

When done.... you still might like the stock sound anyhow... some do, some don't.

[RC99]

Yes, fixed bias power tubes is a must if you want more power.
No matter what anyone tells you... those amps will not make much more then about 20-24 watts in cathode bias.
Thinning it out is exactly what those amps need to have a more modern sound! ha ha.

Yep..that's pretty much what I came to realize after owning this circuit. It's really great and fat up to about medium club volumes, then just needs more amp to cut through.

YThat paraphase driver adds a certain distortion and "tone" that will limit the clean output power too.
The driver stage distorts before the power tubes....
The contact bias of the octal 6SC7 tubes limits the amp a bit too... and some think they are a little muddy.
You should try 6SC7GTs if you have the metal envelope ones... the glass ones sound better to me.
Drop the 100nF coupling caps to the volume pots to .033uf and change the 500pf treble bypass cap to around 680pF.
I prefer a 2K7-2W screen node resistor in those instead of the 10K.
And, if you go fixed bias, you need to block DC from the grid of the lower triode.... but you can use a GZ34/5AR4 rectifier and set the bias voltage so the power tubes idle around 30ma to 34ma each. That will kick it in the pants.

When done.... you still might like the stock sound anyhow... some do, some don't.

I have it with 6N9Ps/6SL7s.

Y'know...I might just get one of those Bad Cat Unleashes down the road if I have to use this in a larger venue. I actually went with .033 and .022 coupling caps to the volume pots already, which helped. Also wired some bright caps to both channels with switches which does some nice stuff as well. What will the 2K7 in place of the first 10K do? I don't have any 2K7's in 2W, but I have a lot more 10K's...what If I put another in parallel of for 5K?

I might even go with a 5C3P 'Octal Proluxe' and see what that does. Or I might consider a cathode/fixed bias switch if possible. Thanks again, Bruce....you're always very generous with your know-how.

one last question...this amp pops when I put it on standby. I've read about this in other forums, and it seems that it's not a big deal...and you don't hear it when I turn the volume down. I tried a new Carling switch and it does the same. It does have the .047uf 'snubbing' cap to ground on the node that has a lead to the rectifier, should I take it off?

Edit: wired a 120pf in parallel with the 500pf treble cap and I like it.

[pdf64]

'The driver stage distorts before the power tubes'
What is causing that?
On the face of it, that paraphase should have a large output voltage swing available (unless the operating point is wacky).
http://www.webphix.com/schematic%20h..._5c5_schem.pdf
Pete

[RC99]

Isn't that kinda' what happens with the stock Princeton Reverb, too?

[Bruce / Mission Amps]

The 5K with two 10Ks in parallel with is fine... it raises the screen voltage on the power tubes and the preamp voltages a tiny bit... while still having some control over the current.
Many of the old tweed amps do not use a high plate voltage on their preamp tubes.
Using 6SL7s types over the 6SC7s means you probably should be using different value plate load resistors though... have you changed that or still using the 250Ks?

The pop is probably because the high voltage slaps on or off, creating a current surge through the power tubes.
I would not think the .47uF cap would make much difference but it will charge up to the full ripple voltage of the rectifier output... probably around 420vdc.
Maybe move it across the two contacts of the switch?
**************

Paraphase driver (5C5) vs Cathodyne driver (5E3 or BF Princeton)

Yes, if you view the AC outputs of the paraphase driver at high levels, it is quite different looking then a cathodyne driver.

The cathodyne driver is using only one triode, while the paraphase uses two triodes of the same envelope.
The output of the top triode in the paraphase is sampled and divided across the 3 grid load resistors of the power tubes... then fed into the second half of the dual triode phase inverter, who's output now drives the other power tube.
Both power tubes are being plate fed at a higher Zed then the cathodyne driver's cathode follower.
That creates a different distortion then the 5E3's cathodyne driver, who's cathode follower section effects it's power tube in a way the paraphase can not.

[RC99]

The 5K with two 10Ks in parallel with is fine... it raises the screen voltage on the power tubes and the preamp voltages a tiny bit... while still having some control over the current.
Many of the old tweed amps do not use a high plate voltage on their preamp tubes.
Using 6SL7s types over the 6SC7s means you probably should be using different value plate load resistors though... have you changed that or still using the 250Ks?

Hi and thanks again, Bruce. I'm using the Weber version....

http://www.diyrecordingequipment.com...e5a_layout.jpg
http://taweber.powweb.com/store/5c5_schem.jpg

Looks like 250ks...what should they be instead....150k?

I added another 10K in parallel to the first screen node resistor, seems fine.

The pop is probably because the high voltage slaps on or off, creating a current surge through the power tubes.
I would not think the .47uF cap would make much difference but it will charge up to the full ripple voltage of the rectifier output... probably around 420vdc.
Maybe move it across the two contacts of the switch?

I'll give that a try, thanks. I'm also looking into a Fixed/Cathode bias switch. I'll diagram it out and post it for advice. I'm trying to figure out where the lead from the bias pot's middle lug goes to. On a 'Proluxe', it goes to the two 220ks on the phase inverter's caps and connected to the grids on the power tubes.

http://taweber.powweb.com/store/5e3p_layout.jpg

On the 5C5, I'm wondering if it goes to the lone 250k which connects to only one of the power tube's grids, breaking the connection to the cathode resistor's ground.

Edit: went with an .047µF across the terminals on the standby switch and that seems to be the ticket. No more popping, and it seems to 'fade' into standby as opposed to switching hard into it. I hope that's healthy....I like it.

[Bruce / Mission Amps]

Hi and thanks again, Bruce. I'm using the Weber version....

http://www.diyrecordingequipment.com...e5a_layout.jpg
http://taweber.powweb.com/store/5c5_schem.jpg

Looks like 250ks...what should they be instead....150k?

I added another 10K in parallel to the first screen node resistor, seems fine.



I'll give that a try, thanks. I'm also looking into a Fixed/Cathode bias switch. I'll diagram it out and post it for advice. I'm trying to figure out where the lead from the bias pot's middle lug goes to. On a 'Proluxe', it goes to the two 220ks on the phase inverter's caps and connected to the grids on the power tubes.

http://taweber.powweb.com/store/5e3p_layout.jpg

On the 5C5, I'm wondering if it goes to the lone 250k which connects to only one of the power tube's grids, breaking the connection to the cathode resistor's ground.

Edit: went with an .047µF across the terminals on the standby switch and that seems to be the ticket. No more popping, and it seems to 'fade' into standby as opposed to switching hard into it. I hope that's healthy....I like it.

Your paraphase circuit will need the -DC bias voltage applied to where the smaller value resistor, 6K8 to 10K, is grounded. Lift it from ground of course and apply the bias voltage there.
Then use a DC blocking cap on the grid of the lower 6SL7 triode to keep bias voltage off of "it" and solder a fixed 500K to 1M 1/2w resistor on the grid lug to ground, right at the socket.

[RC99]

Excellent...much thanks. Been trying to do some research to see what value plate load resistors to change the 250ks from. Which would you choose, and for more or less gain?

[loudthud]

Note that any ripple (hum) on the bias supply gets injected into the grid of the lower tube of the phase inverter, so you will need a little extra filtering on the bias supply.

[Bruce / Mission Amps]

Note that any ripple (hum) on the bias supply gets injected into the grid of the lower tube of the phase inverter, so you will need a little extra filtering on the bias supply.

Correct again!
Glad someone is watching.
I use an additional reverse polarity, 22uF@100v cap right at the junction of the low value resistor... good call!

Plate load resistors for 6SL7s:
I've used anything from 120K to 160K with those 6SL7s... but I've also used 220K to 270K.... my preference would be the lower valued ones.
A might get a little push back here, but with the octal preamp tubes.... I always avoid any carbon comp resistors like they are the plague!!

[RC99]

Thanks Loud and Bruce. I'll post a layout diagram of the bias circuit I'm hoping to build in another...it seems like too much to do as a switch in this. Bruce, luckily I have Carbon Film and Metal resistors throughout. Went with 160K...seemed to bump up the gain a bit, maybe a bit too much and increased the feedback, so I went to 220K and seem to like it. Would it be dangerous/damaging to try a GZ34 rectifier with this? I'm currently using the Weber 5U4 Copper Cap, 413V B+, 409V Plates, 25.8V across the cathode resistor.

Edit: tried a GZ34.....428V B+, 424V Plate, 29.12V across cathode R.

Anyway, I'm so glad I resurrected this build...almost forgot how much I loved it. The original cab was used for a Bassman I built a while back because I needed more power for outdoor and larger gigs...sold it later on. But this circuit is such a gem...maybe more Ampeg than Fender Tweed in a lot of ways...but it's such a smooth, warm inherent tone. Nicer cleans than a Blackface, IMO. Actually, my 'normal' channel with a 120pf bright cap turned on is rather BF-ish (or maybe Ampeg) in that it has a deeper bottom but with the higher treble and .022µf coupling cap, a more 'scooped' midrange. Whereas the 'bright' with the .033µf is more of a fat-mids classic tweed. Going to both inputs, they mix really nicely and it gives you some good shaping options for different guitars. My ES-335 sounds unbelievable through it. Only niggle is that it feeds back pretty easily, but that's probably due to my lead dress as this is one of my earlier kits. Still controllable, though.