Benson Monarch

[Synchu]

Looking at the schematic Tweed Deluxe was my guess as well and I ordered a Tweed Deluxe set the next day the schematic was posted. Now I have all the parts for some time already, but not the time to build it just yet

Niki

[unknowntome]

Hey everyone - just touching base as ive done my best to add the power section to the layout that BobL posted. I've cut and paste the power section from the 5e3 layout on Rob Robinettes site which has been an invaluable resource for me and no doubt loads of others. I was hoping someone could take a glance and let me know if it looks ok? Im really in the beginning stages of getting into DIY tube amps having spent most of my focus on pedals. Cheers!

https://imgur.com/seo1xTe

[BobL]

Hey everyone - just touching base as ive done my best to add the power section to the layout that BobL posted. I've cut and paste the power section from the 5e3 layout on Rob Robinettes site which has been an invaluable resource for me and no doubt loads of others. I was hoping someone could take a glance and let me know if it looks ok? Im really in the beginning stages of getting into DIY tube amps having spent most of my focus on pedals. Cheers!

https://imgur.com/seo1xTe

I would take both PT center taps to the same ground lug.

Your AC cord will go to one side of the fuse and one side of the switch, then your common and wall voltage taps from your PT will go to the other side of the switch and the fuse.

I built w/o a standby switch, so that was different on mine.

If you can find a PT that is putting out less voltage, you will get closer to the measured voltages - I used 300v taps on mine with a 5Y3, and hit pretty much on the money, voltage wise.

[Awiles]

Looking at the dizzy bird schematic and what Chris added, has anyone found the issue with the output buffer that Chris noted?
Thanks,
Adam

[unknowntome]

Hey everyone - just touching base as ive done my best to add the power section to the layout that BobL posted. I've cut and paste the power section from the 5e3 layout on Rob Robinettes site which has been an invaluable resource for me and no doubt loads of others. I was hoping someone could take a glance and let me know if it looks ok? Im really in the beginning stages of getting into DIY tube amps having spent most of my focus on pedals. Cheers!

https://imgur.com/seo1xTe

I would take both PT center taps to the same ground lug.

Your AC cord will go to one side of the fuse and one side of the switch, then your common and wall voltage taps from your PT will go to the other side of the switch and the fuse.

I built w/o a standby switch, so that was different on mine.

If you can find a PT that is putting out less voltage, you will get closer to the measured voltages - I used 300v taps on mine with a 5Y3, and hit pretty much on the money, voltage wise.

Hey BobL - thanks heaps for the reply.. that's really helpful.

The stewmac 5e3 instructions have the power transformer installed the way you've described.

https://imgur.com/Wgg2rAR

With regards to the standby switch, I suspect the way I've got it wired up should work as intended? Again, this is based on Rob Robinettes 5e3 layout.

The PT voltages written on the layout I posted are from the 5e3 build/layout... ignore those. Although, I am looking at sourcing the tweed deluxe transformers as they seem to be well matched.

Cheers
Tom

[pullshocks]

I've got the Monarch circuit running on my mini-breadboard. I did not do the DC heaters, and I added screen resistors. The PT is a 265-0-265, giving plate voltages about 15 volts lower than those on the schematic.
I have the PI trimmer on the front panel. Volume (and hum) increase as it is rotated from left to right. Need time to explore that more
For V2 I have a 7247, which is supposed to be an ok substitute for a 12DW7.
As mentioned in my earlier posts on page 3, the only reverb tank I have on hand is a 4FBxxx. As suspected, it is not well matched for the cathode cap drive. I can hear some reverb with the control on 10, but it is pretty subtle. But what there is sounds good. I'll probably try changing to a plate drive circuit that is supposed to work well with the xFBxxx type tank. Or order an xEBxxx tank.

I was not able to turn it up above 2, but so far I find it pretty enchanting.

P1010610.jpg

P1010608.jpg

[pullshocks]

Based on some discussion on the Hoffman forum, I replaced the 250pF reverb output coupling cap with a larger value--0.005 uF. This gives a lot more verb, and a lot better reverb tone. It was very bright and harsh with the 250pF.

Bob L hasn't posted here for a while but apparently he has confirmed that the xEBxxx tank is the way to go.

The good news for me is the xFBxxx tank does work and sounds good, despite not being the best match.

The amp is way too loud for my needs, but sounds really good. I've got it hooked up to a Celestion G12H30 (75Hz), as used in many of the demos that can be found on line.

I may look into building an attenuator as designed by John H on the Marshall forum. Or try a lower watt version

[BobL]

The amp is way too loud for my needs, but sounds really good. I've got it hooked up to a Celestion G12H30 (75Hz), as used in many of the demos that can be found on line.

I may look into building an attenuator as designed by John H on the Marshall forum. Or try a lower watt version

When I was running it into a pair of P12Qs it was pretty dang quiet... Maybe an option? That is my go to move for 'too loud'... That and using pedals to gain stage/turn down. I had to get more efficient speakers for it to hang with the band (Eminence GA SC-64s, which sound great with it).

[ViperDoc]

Nice design: a 110k 2k2 stage with half the resistor values on the first stage to increase low order harmonics, and a drastic split load on the second that is like having a volume pot at 5 but with way more bandwidth (and a bit more noise from the psu node), with a very low loss between first two stages.

Hi Roberto, would you mind elaborating on this comment, particularly about the low order harmonic design? It sounds very interesting, thank you!

[BobL]

Based on some discussion on the Hoffman forum, I replaced the 250pF reverb output coupling cap with a larger value--0.005 uF. This gives a lot more verb, and a lot better reverb tone. It was very bright and harsh with the 250pF.

Bob L hasn't posted here for a while but apparently he has confirmed that the xEBxxx tank is the way to go.

The good news for me is the xFBxxx tank does work and sounds good, despite not being the best match.

The amp is way too loud for my needs, but sounds really good. I've got it hooked up to a Celestion G12H30 (75Hz), as used in many of the demos that can be found on line.

I may look into building an attenuator as designed by John H on the Marshall forum. Or try a lower watt version

I replaced the 250pF with a 500pF (this is what it looks like was here in the pic Aaron posted of the preamp), and then after your post I put a .0047pF in there, which helped and provided more reverb... then I replaced the .022uF on the input with a .01uF, and that darkened the reverb in a really nice way.

Still having a very large amount of non-volume specific 60hz hum... might need to try to figure out the DC heaters on the pre to see what that does?

EDIT: I spoke too soon - the two changes above seem to have introduced an oscillating/repeating click into the amp, and, I think, increased hum... that may have only started when I put the .1uF cap on the input of the reverb, so I might try splitting the difference and putting in a .047uF there if I have one...

[dorrisant]

3. I show a 470K resistor in series with the .022uf coming off of the plate on V1 in the schematic, but didn't see this in dorrisant's layout - was this a purposeful omission?

I finally got around to updating the drawings I posted on page 3. Sorry for any confusion.

[Masco]

Dorrisant- you might want to check your powering of the first two stages as well. It appears you have first stage as split plate, instead of second. Check schematic and photos.

[dorrisant]

Good eye... changed that too.

[pullshocks]

Dorrisant-

For the reverb return triode, Rk is shown as1k0 on the schematic. In the picture on page 6 of this thread, it appears to be red-red-red, 2.2K.

Also the reverb return coupling cap is shown as 250pF. Looking at the picture, some think it is 500 pF. I currently have a 0.005 uF in that position, have not tried the 500pF yet, but I think you will find a value larger than 250 pF gives more verb and a fuller reverb sound. Of course you will decide what works best for you.

Looking forward to hearing how you and other builders do as far as hum issues.

I love the sound of the amp but, I am currently getting more hum (120 hz) than I would hope for, with the nothing plugged in the input, and volume on 0. I am working my way through the possible causes and cures. It is not noticeable while playing, but is annoying when not playing.

The hum level does vary with the position of the PI balance pot. By turning the pot so it gives 0 ohms to ground, the hum is lowest. But as I understand it, in that condition no signal is going to that side of the power amp, and as you would expect, the volume is lower. According to the Ampbooks paraphase calculator, https://www.ampbooks.com/mobile/amplifi ... paraphase/ a resistance of about 4K to ground should give a balanced signal to both power amp tubes, so I am using that as my default setting.

I tried running the preamp heaters with DC as shown in the schematic. I found that it had an effect on noise with the volume all the way up, but did not affect the baseline hum with volume on 0. If I do a permanent build I will probably include the DC heaters. It is in breadboard form right now.

One last comment on the DC heaters. The schematic shows the "negative" DC leg tied to ground. That is how I wired it. But in the photo on page 6 of this thread, there are a couple of 100 ohm resistors visible at the rectifier/capacitor unit, so maybe the DC is referenced to ground with those resistors.

[Synchu]

If your power transformer has center tapped filament secondaries and you connected the center tap then the 100 Ohm resistors should not be used.
I would try the DC heaters with 100 Ohm reference resistors with the center tap not connected.
Niki