Benson Monarch

[Synchu]

While on the reverb subject, I changed the 8FBxx tank (I was using) with an 8EBxx, since I found use for the FB in athoer project - the difference is rather tiny

Niki

[dorrisant]

Guys, where is the latest and greatest schematic located?

[CraigGa]

So I've finally got my build almost finished and it's sounding great.
I had some issues with hum but I've got rid of almost all of that now, the biggest gain there was moving the PI to gnd 4 from gnd 3.

I'm also getting the bleed through at zero volume issue that others have had, has anybody found a definite fix for that before I start scoping around in there? I think that I've determined that the source is the first triode but where it's getting back into the signal path I'm not sure yet. It's not related to the reverb because it's the same with the reverb tube pulled.

Craig

[CraigGa]

Guys, where is the latest and greatest schematic located?

I'm not sure that mine is either but I can send you a copy if you want?

Craig

[Synchu]

Guys, where is the latest and greatest schematic located?

I used that one on page 2 and I think it is still the accepted latest with few notes - later amps have had 0.1uF coupling caps changed for 0.02uF (but this can be subjective so a bit of experimenting is advisable).
I added also an additional power supply note for the reverb stage - as it has been discussed here - kinda sounds better to my ears and also adjusted the power string to go with my higher PT voltages (plus that I am using 5Y3 rectifier). Might have (unlikely) tweaked few other cap values - but can't really remember

Niki

[mikeywoll]

Guys, where is the latest and greatest schematic located?

I used that one on page 2 and I think it is still the accepted latest with few notes - later amps have had 0.1uF coupling caps changed for 0.02uF (but this can be subjective so a bit of experimenting is advisable).
I added also an additional power supply note for the reverb stage - as it has been discussed here - kinda sounds better to my ears and also adjusted the power string to go with my higher PT voltages (plus that I am using 5Y3 rectifier). Might have (unlikely) tweaked few other cap values - but can't really remember

Niki

This is my up to date version... has the extra reverb ps node, just swap the rectifier for tube and remove the extra VVR caps/resistors if not interested.

https://ampgarage.com/forum/viewtopic.p ... &start=372

[bodhi]

Hi everyone, thanks for the amazing resource and doing a lot of work to get these builds working!

I'm fairly new at amp building and working on a Dizzy Bird. I've had the Vinny part working well as far as I can tell for about a a week now, but the tall bird reverb section is giving me problems... For some reason I got it into my head that it would also be a 12dw7 reverb, but reading the thread again I rewired it with a 12au7 in my testbed (aluminum cake pan). In both cases the dry path works, but I don't get reverb signal from the guitar itself and the whole system squeaks and oscillates if I turn up the Dwell pot more than to not kill the dry signal. The return path seems to work with both wirings, as I get a decent sound slamming the reverb tank itself...

Looking at the pictures shared of the Dizzy Bird guts earlier; https://ampgarage.com/forum/viewtopic.p ... 87#p432487 --- are both the transformers on the inside of the chassis there, or is in fact one of them a reverb transformer?? I've yet to wrap my head around the layout, so can't tell yet...

The power transformer that I'm using might be putting out too high voltages for the amp, but that doesn't seem to affect the Vinny part... Could that be enough reason for the oscillations? I've tested with another (similar) reverb tank, and neither gets signal.

My current layout is with the reverb wet path as 12ax7 triode -> 12au7 (both sides) -> reverb tank -> 12ax7 -> 12ax7 output, but as mentioned I got similar results with two 12ax7 triodes going into the 12au7 side of the 12dw7 and then the reverb tank...

[pompeiisneaks]

Hi everyone, thanks for the amazing resource and doing a lot of work to get these builds working!

I'm fairly new at amp building and working on a Dizzy Bird. I've had the Vinny part working well as far as I can tell for about a a week now, but the tall bird reverb section is giving me problems... For some reason I got it into my head that it would also be a 12dw7 reverb, but reading the thread again I rewired it with a 12au7 in my testbed (aluminum cake pan). In both cases the dry path works, but I don't get reverb signal from the guitar itself and the whole system squeaks and oscillates if I turn up the Dwell pot more than to not kill the dry signal. The return path seems to work with both wirings, as I get a decent sound slamming the reverb tank itself...

Looking at the pictures shared of the Dizzy Bird guts earlier; https://ampgarage.com/forum/viewtopic.p ... 87#p432487 --- are both the transformers on the inside of the chassis there, or is in fact one of them a reverb transformer?? I've yet to wrap my head around the layout, so can't tell yet...

The power transformer that I'm using might be putting out too high voltages for the amp, but that doesn't seem to affect the Vinny part... Could that be enough reason for the oscillations? I've tested with another (similar) reverb tank, and neither gets signal.

My current layout is with the reverb wet path as 12ax7 triode -> 12au7 (both sides) -> reverb tank -> 12ax7 -> 12ax7 output, but as mentioned I got similar results with two 12ax7 triodes going into the 12au7 side of the 12dw7 and then the reverb tank...

Usually it's best to send some screenshots of the amp with the detailed shots around the parts that don't seem to work correctly. If you've accidentally reverse wired the reverb pan, yes it will not work. This particular reverb tank is not transformer driven, so you need the right impedance type. On the other hand, this whole thread is built around the monarch, so the dizzy bird may be massively different. The best bet might be to start a new thread with what you've built, how you know this amp so far is 'right' (i.e. schematics you're following and/or layouts) so people can review and suggest tips/tricks/fixes.

~Phil

[CraigGa]

I've been trying to diagnose the bleed through at zero volume issue.

I proved that the bleed signal is present at the input to the PI,
Disconnecting the lower plate resistor to the second triode of cause kills the main signal but the bleed signal is still present at any volume pot setting,
This led me to believe that the bleed signal is coming from the B+ via the upper plate resistor so the only possible source is the input triode plate resistor.
I tried powering the input triode from a different node and/or increasing the plate resistor to 100K.
The only combination I can find that eliminates the bleed completely is with 100K plate resistor and powering that from the extra reverb filter node.

Has anyone got any other suggestions?

[mikeywoll]

I've been trying to diagnose the bleed through at zero volume issue.

I proved that the bleed signal is present at the input to the PI,
Disconnecting the lower plate resistor to the second triode of cause kills the main signal but the bleed signal is still present at any volume pot setting,
This led me to believe that the bleed signal is coming from the B+ via the upper plate resistor so the only possible source is the input triode plate resistor.
I tried powering the input triode from a different node and/or increasing the plate resistor to 100K.
The only combination I can find that eliminates the bleed completely is with 100K plate resistor and powering that from the extra reverb filter node.

Has anyone got any other suggestions?

You're giving me deja vu... I spent many hours hunting the source of that signal. I couldn't come up with a solution that didn't drastically alter the playability of the amp. I finally just accepted it as a drawback of the design.

I came to a similar conclusion, in part, as you did regarding the source. I think the signal bleeds a couple of ways. One way is through the plate resistor, as you found. I moved the triode to the PI node. It killed the bleed, but introduced hum and made the amp more stiff. Also folks noticed that disconnecting one side of the reverb tank also fixed the issue. I think the cathode follower is also letting signal through, maybe depending on loading. This may be better with the 5th PS filter cap... I haven't checked.

[CraigGa]

You're giving me deja vu... I spent many hours hunting the source of that signal. I couldn't come up with a solution that didn't drastically alter the playability of the amp. I finally just accepted it as a drawback of the design.

I came to a similar conclusion, in part, as you did regarding the source. I think the signal bleeds a couple of ways. One way is through the plate resistor, as you found. I moved the triode to the PI node. It killed the bleed, but introduced hum and made the amp more stiff. Also folks noticed that disconnecting one side of the reverb tank also fixed the issue. I think the cathode follower is also letting signal through, maybe depending on loading. This may be better with the 5th PS filter cap... I haven't checked.

I built mine with the reverb filter cap and I'm confident that the reverb is not a source, like you I tried powering from the PI and had the same results but seeing that I've done a lot of work to get hum to a minimum I didn't want to go there again.

Am I correct in thinking that increasing the plate resistor to 100k will increase the gain?

I'll keep experimenting but thanks for confirming my findings so far.

Craig

[bodhi]

Hi everyone, thanks for the amazing resource and doing a lot of work to get these builds working!

I'm fairly new at amp building and working on a Dizzy Bird. I've had the Vinny part working well as far as I can tell for about a a week now, but the tall bird reverb section is giving me problems... For some reason I got it into my head that it would also be a 12dw7 reverb, but reading the thread again I rewired it with a 12au7 in my testbed (aluminum cake pan). In both cases the dry path works, but I don't get reverb signal from the guitar itself and the whole system squeaks and oscillates if I turn up the Dwell pot more than to not kill the dry signal. The return path seems to work with both wirings, as I get a decent sound slamming the reverb tank itself...

Looking at the pictures shared of the Dizzy Bird guts earlier; https://ampgarage.com/forum/viewtopic.p ... 87#p432487 --- are both the transformers on the inside of the chassis there, or is in fact one of them a reverb transformer?? I've yet to wrap my head around the layout, so can't tell yet...

The power transformer that I'm using might be putting out too high voltages for the amp, but that doesn't seem to affect the Vinny part... Could that be enough reason for the oscillations? I've tested with another (similar) reverb tank, and neither gets signal.

My current layout is with the reverb wet path as 12ax7 triode -> 12au7 (both sides) -> reverb tank -> 12ax7 -> 12ax7 output, but as mentioned I got similar results with two 12ax7 triodes going into the 12au7 side of the 12dw7 and then the reverb tank...

Usually it's best to send some screenshots of the amp with the detailed shots around the parts that don't seem to work correctly. If you've accidentally reverse wired the reverb pan, yes it will not work. This particular reverb tank is not transformer driven, so you need the right impedance type. On the other hand, this whole thread is built around the monarch, so the dizzy bird may be massively different. The best bet might be to start a new thread with what you've built, how you know this amp so far is 'right' (i.e. schematics you're following and/or layouts) so people can review and suggest tips/tricks/fixes.

~Phil

Yeah, I guess, the schematics were shared earlier in the thread with the Monarch ones so I thought it might be a good place to ask, but you have a point.

[CraigGa]

So I've done more experimentation around the bleed issue and found that,

I can't cure it with anything less than 100K in the first triode plate.
Decoupling the first triode power with 0.1uF capacitors does nothing.

So I have made mine permanent, replace the first triode plate resistor with 100k and power it from the additional reverb power node.
There is absolutely no bleed and hum wasn't affected.

I injected a signal that resulted in 1V after the first triode decoupling capacitor and when I'd changed the resistor it went up to 1.15V but seeing as this ultimately feeds the volume pot I can't see any issues.

Hope this helps someone else.

Craig

[mhat]

Just saw this on reverb. Another gut shot of the Benson Monarch Reverb. I haven't dug into, but there are definitely some more filter caps in there.

[mikeywoll]

Just saw this on reverb. Another gut shot of the Benson Monarch Reverb. I haven't dug into, but there are definitely some more filter caps in there.

Could it be that the 1st triode of V1 (56K) feeds the reverb cathode follower across the 220k resistor, and the split plate (with 4.7K) feeds the additional cap and reverb recovery triode via the 4.7K spanning the gap to the additional filter cap? Hard to tell what's going on in there? Otherwise it matches up with my schematic.

Edit never mind, I think it's just a 4.7K dropping resistor (I guessed 2.2K based on the other images). So 4.7K/100K split plate and 4.7K dropping on this one vs 5.6-10K/100K and 2.2K dropper on my schematic.