Another Toroidal PT AC30 clone

[lord preset]

I haven’t built anything in a while but I am finally getting around to making myself a lighter, cheaper AC30 clone. I made one for a friend back in 2015 https://ampgarage.com/forum/viewtopic.p ... cheap+ac30 and liked it a lot. This time I’m working from the Hoffman AC30 schematic but not the layout, a stiffer Rocket power supply, SS rectifier, and I’m cramming it into a 16x7 Fender style chassis. I thought about using the same Fender HRD OT I used on the previous build but I already have a Classitone AC30 OT I picked up long ago that pleaded to be used so I could not refuse despite the weight. I will still save pounds with the Antek PT, a small pine cab and a Celestion neo speaker. There will be a single input jack feeding both the Top Boost and Normal channels and I want to be able to select either or both (in parallel) on a switch. I haven’t figured out the details on that or on how to get both channels in phase. Too much fun.

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[pompeiisneaks]

Good stuff, I love the AC30, still my favorite amp.

~Phil

[Roe]

We should try an ac30 with a switching power supply that delievers 6.3VDC and 320VDC

[sluckey]

There will be a single input jack feeding both the Top Boost and Normal channels and I want to be able to select either or both (in parallel) on a switch. I haven’t figured out the details on that or on how to get both channels in phase.

Here's how I used a C&K 7211 ON-ON-ON switch to select either channel or both channels...

http://sluckeyamps.com/phoenix/phoenix.pdf

And here's an easy way to get the channels in phase. Rather than use 220K mixing resistors as Hoffman did, just connect each channel to separate inputs on the LTP PI. Like this...

http://sluckeyamps.com/dual_lite/dual_lite.pdf

[xtian]

Is this a tubes-down build? Suggestion: Leave a little room at the edges of the chassis, around the trannys, so you can slide the chassis into the cabinet on rails.

[lord preset]

There will be a single input jack feeding both the Top Boost and Normal channels and I want to be able to select either or both (in parallel) on a switch. I haven’t figured out the details on that or on how to get both channels in phase.

Here's how I used a C&K 7211 ON-ON-ON switch to select either channel or both channels...

http://sluckeyamps.com/phoenix/phoenix.pdf

And here's an easy way to get the channels in phase. Rather than use 220K mixing resistors as Hoffman did, just connect each channel to separate inputs on the LTP PI. Like this...

http://sluckeyamps.com/dual_lite/dual_lite.pdf

Thanks on both counts. I am ordering the switch. I was on the fence about just omitting the normal channel altogether ( I never use it on my Hayseed 30) but the blending option sounds possibly useful.

[lord preset]

Is this a tubes-down build? Suggestion: Leave a little room at the edges of the chassis, around the trannys, so you can slide the chassis into the cabinet on rails.

Too late for that but I did install cage nuts so getting the chassis in should be relatively easy.

[lord preset]

I haven't done this in a while and forgot how many mistakes I always make. I didn't wait long enough before clear coating the chassis decals and the whole thing wrinkled up and has to be redone. While waiting for the paint to thoroughly dry and parts to arrive I got started on the power supply. Again I forgot how fiddly it is to work around the large footprint of the toroidal PT to find mounting points. After coming up with a workable size and shape I drilled the eyelets on the wrong side so there are now many ventilation holes to keep things cool. I had not forgotten how much I hate heater wiring but I am anxious to see how feeding the power tube and preamp tube from separate filament taps works out. Antrek provides two 3 amp 6.3v taps but in the last two builds I just ran them in parallel.

[sluckey]

Are those four sockets shown above for the power tubes? If so, you'll want to rewire the filaments.

[lord preset]

Are those four sockets shown above for the power tubes? If so, you'll want to rewire the filaments.

Of course I will. I was just testing you.

[lord preset]

Wiring is done. Now comes the all important Fretting and Staring ™ phase of the build where I ponder what I have done wrong before moving to the light bulb test. This phase can take days. After several attempts I final got the ON-ON-ON switch suggested by sluckey installed. A while back I bought a roll of shielded wire off eBay that has turned out to be more trouble than it is worth. It's quite stiff and the braid is very tight and hard to untangle. The stiffness of the wire meant that as I tried to get everything into place too much stress was put on the delicate connections to the switch and the 24ga inner core wires broke. Twice. Next time I'm going back to RG174.

[joeboo88]

Looking good! I might copy how you laid everything out.

I am also about to build one, I have everything I need, I hope it sounds different from my Rocket.
I’m gonna put a MV in mine

Can’t wait till it’s done....keep going

[lord preset]

The Fretting and Staring ™ phase has already paid dividends. I was staring at the filter caps and it occurred to me that they would be more effective if they were connected to something.

[joeboo88]

The Fretting and Staring ™ phase has already paid dividends. I was staring at the filter caps and it occurred to me that they would be more effective if they were connected to something.

LOL

[lord preset]

It passed the lightbulb test so I fired it up this AM. It is loud as #%#, but all is not yet as it should be:

1. It's also noisy as ##$#. I haven't started working on this yet but I expect it will take a while to sort out.
2. Unlike my last build where the Normal channel was too dark and the TB channel was just right, now the Normal channel sounds good and the TB channel is too shrill. I removed the bright cap which helped but it still needs work.

The major differences in this build vs the 1st one are 1) the addition of the channel switch and 2) the use of a 275v PT (which I had on hand) vs the 230V PT on the 1st build. I am getting ~330v on the plates and 325v on the screens which is not out of line by tube cooking AC30 standards but the last version has 290v/285v.

One question I have which may concern either, both or neither of my issues is that when sending the channels to opposite sides of the LTPI to get them in phase I omitted the 220K mixing resistors, but I notice on the TW Rocket schematic there is 220K resistor before the coupling cap even though there in just one channel. Should I have left them in?