Benson Monarch

[mikeywoll]

Hum is now GONE!!!

Even with AC heaters, and breadboard construction. Ran the PT 6.3 V center tap to the 6V6 cathode connection.

DC heaters may be even better.

Sorry for any confusion caused by my post yesterday. I will edit accordingly.

I can confirm that that elevating the heaters worked well to quiet the amp down as an alternative to D/C heaters. That was a great idea!

Mike

[T Wilcox]

Just fired up my Monarch reverb build for the first time and other than I wired up all the pots reverse everything seems to be working as it should
This was my first true point 2 point build. I gutted a trainwreck express build I did back in 2011 that I never quite bonded with and used the chassis, had faceplates I designed made by Steve at INDCOM
Heres a link of me noodling while turning some knobs through a Dumble style 2x12 with WGS ET65 and a VET30, it was getting late so I didn't turn it up too loud in my garage (dont forget the knobs are wired backwards so 0=10 or clockwise = off)
https://youtu.be/3RLGnTdWxvk
I plan on re-wiring the pots tomorrow
I also will be building a combo cabinet so I searched around for a good speaker to pair with this amp and ran right into the best option I could ask for https://www.bensonamps.com/speakers/custom%20ceramic
I think the best part of this build was when @ChasBenson chimed in and set us straight on the power section. That is the coolest!
The Dwell knob and boost switch and standby are not wired in yet. wanted to hear the original circuit first

[BobL]

I finally grabbed a few minutes this morning to update the layout I made with all of the changes from this thread...

Attached are the new layout and a version where I marked the areas that changed.

Will update the original location of the layout as well - let me know if I'm missing something still...

I plan to try and implement these changes and see where I end up.

Hi BobL,

Thanks for updating the layout. It takes a lot of work. I think we got this one pretty much dialed in.

I noticed a couple things that are off on the updated schematic...

1) The phase inverter is still messed up on this one. It's a confusing design. Start with your original layout, then swap the wires connected to pin 2 and pin 7 of V2. That will work.

Yeah, this is what I intended to do... and I swapped 2 and... 6. Oops. Updated with 2 and 7.

2) The 100K resistor at the right most "D" node (the plate resistor for V3) connected to the 500pf capacitor should be 470K.

Ah, yep - missed that one.

3) This one is a little more of a style thing, and I apologize if its one you know.... In general, grid resistors should go directly on the tube pins, with as short a lead between the resistor and pin, as possible. They act to suppress RF in that configuration. It also saves space on your board. Often times, "Buzz" is just stray RF that gets amplified, and relocating resistors to the grid pins can make a huge difference in quieting an amp. I live near a radio tower. If I put my grid resistors anywhere other than on the tube, I end up with a great AM/FM radio. I can tune channels with the tone and volume knobs!

I linked a great resource here: https://www.aikenamps.com/index.php/gri ... -they-used

I guess I've just never built an amp that did that before - seems like most Fender amps have that 68K on the input as in the layout?

I'll keep that in mind if I'm noticing noise once I've implemented the other changes.

Thanks for the feedback - other changes made.

[pullshocks]

searched around for a good speaker to pair with this amp and ran right into the best option I could ask for https://www.bensonamps.com/speakers/custom%20ceramic
I think the best part of this build was when @ChasBenson chimed in and set us straight on the power section. That is the coolest!
The Dwell knob and boost switch and standby are not wired in yet. wanted to hear the original circuit first

The Benson custom seems like a sure bet for a speaker. I went straight to my old G12H30 recone and it just seems really right with this amp. Have also tried an Eminence Cannabis Rex and its good too.

Curious what you have in mind for the boost switch.

[T Wilcox]

At the very least it's a little throwback to Benson for chiming in on this thread so when I saw that speaker available I had no second thoughts
For the boost, now that I have it up and running I will try a few things before settling but I was thinking about switching in a 5uF or lower instead of 25uF(25u would be the boost) for V2A cathode bypass or possibly add a cathode bypass cap for V2b. To be determined really
I kept the same holes as the TW Express had for the faceplate so without having played the Monarch I figured I'd leave room to add on

[dorrisant]

Nice catch on that switch Mike.

T Wilcox - very nice looking p-to-p there! Looks beautiful.

I will try to find some time to update my layout soon. Looks like you guys have sorted most everything out. Awesome!

[T Wilcox]

Thank you Dorrisant

[mikeywoll]

Just fired up my Monarch reverb build for the first time and other than I wired up all the pots reverse everything seems to be working as it should...

I think that may sound better than the real thing. Excellent playing too. I really like the little touches you put in there also like the diodes on the rectifier. That tone has me convinced... Save your pennies on carbon comp resistors and put them towards better iron. What output tranny are you using? That thing looks beefy!

Mike

[mikeywoll]

I finally grabbed a few minutes this morning to update the layout I made with all of the changes from this thread...

Attached are the new layout and a version where I marked the areas that changed.

Will update the original location of the layout as well - let me know if I'm missing something still...

I plan to try and implement these changes and see where I end up.

Hi BobL,

Thanks for updating the layout. It takes a lot of work. I think we got this one pretty much dialed in.

I noticed a couple things that are off on the updated schematic...

1) The phase inverter is still messed up on this one. It's a confusing design. Start with your original layout, then swap the wires connected to pin 2 and pin 7 of V2. That will work.

Yeah, this is what I intended to do... and I swapped 2 and... 6. Oops. Updated with 2 and 7.

2) The 100K resistor at the right most "D" node (the plate resistor for V3) connected to the 500pf capacitor should be 470K.

Ah, yep - missed that one.

3) This one is a little more of a style thing, and I apologize if its one you know.... In general, grid resistors should go directly on the tube pins, with as short a lead between the resistor and pin, as possible. They act to suppress RF in that configuration. It also saves space on your board. Often times, "Buzz" is just stray RF that gets amplified, and relocating resistors to the grid pins can make a huge difference in quieting an amp. I live near a radio tower. If I put my grid resistors anywhere other than on the tube, I end up with a great AM/FM radio. I can tune channels with the tone and volume knobs!

I linked a great resource here: https://www.aikenamps.com/index.php/gri ... -they-used

I guess I've just never built an amp that did that before - seems like most Fender amps have that 68K on the input as in the layout?

I'll keep that in mind if I'm noticing noise once I've implemented the other changes.

Thanks for the feedback - other changes made.

Yeah, the grid resistor placement is not not a universal rule, but in some cases can be necessary. The original amp has them on the tube, which is why I figured it's worth mentioning.

Mike

[T Wilcox]

I think that may sound better than the real thing. Excellent playing too. I really like the little touches you put in there also like the diodes on the rectifier. That tone has me convinced... Save your pennies on carbon comp resistors and put them towards better iron. What output tranny are you using? That thing looks beefy!

Mike
[/quote]

Hey thanks Mike! I ordered the parts for the build before the errors in the schematic were identified so I made some leftover parts work. For example the can cap is a 50/50 from a Ceriatone 50W Plexi Bass kit I built a decade ago (metered at exactly 50uF still) but I only used one section for the 47uF and then used the 3 F&T 22uF's for the rest. The PT and OT is Classictone iron for a Trainwreck build I never loved, as well as the chassis. It sure is beefy, maybe I'll convert it to EL34 one day
I appreciate the your input on the USA/British switch and reverb return plate resistor! Came at the perfect time too
I never even adjusted the phase inverter pot. I'm about to go check voltages and see how adjusting that affects the sound right now

[T Wilcox]

There are 2 thing on the original but not on the schematic that I may add soon here
1. The power switch on the original is a 3way switch with middle position being standby (I didnt wire my standby switch at all)
2. There is a mono jack that shorts the reverb return to ground using TRS for footswitchable reverb

My layout is mirror image to the gut pic Aaron posted because I utilized existing panel holes in my chassis
Here is the layout of mine at this point, I cant post the DIY file because it shows invalid file type but if anyone wants it I'll email it to them

Todd

[BobL]

Yeah, the grid resistor placement is not not a universal rule, but in some cases can be necessary. The original amp has them on the tube, which is why I figured it's worth mentioning.

Mike

Fair enough - part of this specific layout was trying to get things to work into this tweed chassis I was already using, and I'm not sure how well putting the resistors on the sockets would fit?

I'm already not sure how I'm going to add a node to this board, especially w/o yanking it out completely. I ordered some F&T caps to replace the 30uF JJs I used originally, and I think they should be a bit smaller?

Guess we'll see how janky this build ends up.

[T Wilcox]

Here's a good read on grid stopper resistors
TLDR: It is most beneficial to have the input grid stopper mounted directly to or very close to the tube socket, anything between it and the socket becomes an antenna for HF noise
https://www.aikenamps.com/index.php/gri ... -they-used

[T Wilcox]

Here's a video of my observations while adjusting the phase inverter pot for discussion
Oddly the more I balance the signal from the PI into the 6v6's the worse it sounds. My only other experience with PI balance is with Dumble style amps with a Long tail pair PI and the adjustment is very subtle
Both oscope leads are clipped onto the 1k5 power tube grid stoppers
When I say clockwise the pot is shorted, counterclockwise it is 10Kohm
I'd like to hear from others what their thoughts are on whats going on here and how they would find the sweet spot

https://youtu.be/HLP_YHEs1II

Thanks

[mikeywoll]

Here's a video of my observations while adjusting the phase inverter pot for discussion

https://youtu.be/HLP_YHEs1II

Thanks

It's hard to tell looking at your picture it's a little blurry as I zoom in. Are you sure everything is wired up correctly there? It looks like there are 3 wires attached to the pot, there should only be two (the input and the ground). I don't have a scope, so I've just adjusted mine by ear. If I start all the way CCW, it's very noisy. As I rotate CW, I hit a point where the noise drops away suddenly. As I continue rotating CW I get a soft hum that gets louder and louder till I hit max CW rotation. It sounds best at the quietest spot.

Mike