Benson Monarch

[pullshocks]

Finally got a cab built for this thing, still learning the hard way when it comes to tolex and have a few bubbles but it'll do

I like the design. What are the dimensions?

Looks like you received the Benson speaker......

[T Wilcox]

Finally got a cab built for this thing, still learning the hard way when it comes to tolex and have a few bubbles but it'll do

I like the design. What are the dimensions?

Looks like you received the Benson speaker......

Thanks Mike! Hmmm off the top of my head the baffle board was 18x18" then the chassis was 6.5" inside so.. approx 27"H X 19.5"W X 10.5" D with added board thickness
The chassis was more for a head cab but I wanted this one in a combo so I winged it. If I did it again I'd use a proper combo chassis

[CraigGa]

Have you seen this post by Katopan Mike?

https://ampgarage.com/forum/viewtopic.p ... 33#p427333

Craig

Very interesting. I tried disconnecting the volume pot from the second stage and grounding the grid of the tube directly to ground. Signal still bleeds through. It must be happening up at the control pots. In the point to point layout, the controls are pretty far from the circuit and the layout physically separates the various stages. In the turret board layout as I built it, the controls are close to the circuit and different stages are near each other. Plenty of high impedance points near strong signals that allow the opportunity for bleed.

The amp sounds amazing, plays great, and is stable at all volumes. I may rebuild this one in the future, point to point next time

Mike

Which layout did you use Mike?

[mikeywoll]

Have you seen this post by Katopan Mike?

https://ampgarage.com/forum/viewtopic.p ... 33#p427333

Craig

Very interesting. I tried disconnecting the volume pot from the second stage and grounding the grid of the tube directly to ground. Signal still bleeds through. It must be happening up at the control pots. In the point to point layout, the controls are pretty far from the circuit and the layout physically separates the various stages. In the turret board layout as I built it, the controls are close to the circuit and different stages are near each other. Plenty of high impedance points near strong signals that allow the opportunity for bleed.

The amp sounds amazing, plays great, and is stable at all volumes. I may rebuild this one in the future, point to point next time

Mike

Which layout did you use Mike?

I used BobL's layout. My amp looks very similar to his most up to date version, with a couple small changes. I moved a couple resistors off the board onto either the switches or tubes (the cross talk predates these moves). I have added some small ceramic caps to bleed RF at the input jack and from plate to cathode on the first stage and across the reverb recovery stage. I added 10K grid blocking resistors to the reverb tube to snuff RF. My pots are locally grounded at their stages of origin not the pot casing.

Mike

[dorrisant]

Finally got around to building this thing... only to find that the secondary side of my OT is open. Common tap has no continuity to any of the other secondary taps. Shit!!!

Anyone have a Bogen CHA20 OT they'd get rid of?

[T Wilcox]

That looks great Dorrisant! sorry to hear about the OT
Bet it will sound awesome once you get that worked out!

Todd

[dorrisant]

Well, I subbed in a cheap Chinese 2x 6V6 OT and it plays loud and clear.

Voltages are a little off from their targets but not by much... 340v on the 6V6 plates and 328v on the screens, 211v on the first stage plate, 207v on the second stage plate. These NOS CCs are a little off here and there so I will live with it, as is. No reverb in this one and I'm using the 6X6GT from the Bogen since the PT has no 5v tap.

I used AC for the filaments. Tied the filament CT to the power tube cathode pins for elevation. Quiet as a mouse... maybe less.

PI trimmer is set for about 4k.

I'm using what Mike found for the USA/British switch, lots of difference there. Super fat and glassy on the US side. Nice voicing on the British side too.

Gonna have to get a real OT in this thing and play through my good cabs to hear it for sure. Not bad at all though.

HSS Strat was great through it in all positions, each position distinct.

Now to wait for one of these OTs to pop up...

[norburybrook]

Well, I subbed in a cheap Chinese 2x 6V6 OT and it plays loud and clear.

Voltages are a little off from their targets but not by much... 340v on the 6V6 plates and 328v on the screens, 211v on the first stage plate, 207v on the second stage plate. These NOS CCs are a little off here and there so I will live with it, as is. No reverb in this one and I'm using the 6X6GT from the Bogen since the PT has no 5v tap.

I used AC for the filaments. Tied the filament CT to the power tube cathode pins for elevation. Quiet as a mouse... maybe less.

PI trimmer is set for about 4k.

I'm using what Mike found for the USA/British switch, lots of difference there. Super fat and glassy on the US side. Nice voicing on the British side too.

Gonna have to get a real OT in this thing and play through my good cabs to hear it for sure. Not bad at all though.

HSS Strat was great through it in all positions, each position distinct.

Now to wait for one of these OTs to pop up...

that's a great looking build. I've been following this thread. I've never made a point to point amp and this looks like a great projects. I'm also a fan of these kind of 6v6 low wattage amps. I love my tweedle dee for example and use it a lot in the studio.

Chassis and transformers are always the issue though so I'll keep an eye out.

M

[chopstuck]

Dorisant that is the closest thing Ive seen to a silk purse from a sow's ear. I've had that chassis many years ago and came to the conclusion I overpaid for it at $70. From the funky power transformer design with the voltage doubler I didn't understand, to the flimsy sheet metal finger slicing chassis I stripped and had little usable parts left. Kudos to you. It looks grand.

[CraigGa]

Yes it does look great dorrisant,

I was thinking of building mine on tagstrips like my Burman but you've got me thinking now.

[dorrisant]

Thanks guys!

I suggest using the strips. They're what Benson used. More compact than turret boards, so it keeps the area that can pick up noise small.

If you do build it with strips, I have a tip... basically get the stuff that will be on the bottom done first... like all of your wires. Sometimes you can put most of your parts in place while out on the bench, including the wires that will run out to the sockets, etc.. The more you can do to the terminals before you install them, will make for a more enjoyable experience. Also, don't wrap your component leads or wires around the terms too much. If you need to change a part, make it easy on yourself.

Wierd, I have a CNC that produces beautiful pro-quality boards, but I still love the way these go together. Also, the quiet you gain from it.

[CraigGa]

It does look like a good idea.
This is going to be a retirement project so I'm trying not to get too involved until June!

I'm not doing very well so far

Craig

[CraigGa]

Can you clear up a couple of PT questions for me please?

Most designs in this thread appear to be around a 280 0 280V secondary, so is this actually 560v with a centre tap?
I'm used to low voltage transformers like 12-0-12v which could be used for +12v -12v or 24v supplies but 560 *1.414 = nearly 800v

I've seen transformers rated at 30W but does that mean it's for an amp up to 30w output? I've seen somewhere that a 5E3 uses around 75w from the mains.

What secondary current rating should I be looking at for this build?

Thanks
Craig

[T Wilcox]

My 30 watt transformer is an overkill, but its not hurting anything the have it over sized
the 278vac reading on the posted schem is on the AC sideand probably a 280-0-280 with a slight drop due to loading or lower wall voltage
You can multiply the 280 x 1.414 for an approx B+ voltage of 395Vdc then a voltage drop of approx 17vdc using a GZ34. Other rectifiers will drop lower. these voltages with a 5U4GB rectifier (-50vdc)would put the calculated voltages very close to the 333 as per the schem

I am curious what Power transformers others are using though as I might build another similar circuit soon

[CraigGa]

That's what's confusing me,
so you're saying if I measured across the secondary I would see around 280v ac whereas with my 12-0-12 example I would expect to see 24v