B15-inspired Amp Head Build

[JapanAxe]

Over the last few years I have had reasonable success building a handful of small valve amps. I do miss the Ampeg PF-50T that I sold on to purchase an EBS, so the time is right to start possibly my most ambitious scratch build yet. I previously enquired in this thread as to what version of B15 to go for, and I have settled on something close to a single-channel version of the Heritage model (i.e. switchable between 25W cathode bias and 30W grid bias), working from the Ceriatone 'Aunt Peg' layout.

Most of my previous builds have leant heavily on recycling old parts, but this time I am going for quality new parts. I have neither skills nor tools to tackle woodwork, so I am going for a Hammond 'birdcage' style housing. When assembled it is about 12in wide x 10in deep x 7in tall. The transformers (on order from Primary Windings) and valves will all stand up within the mesh cage (proportions not the same as shown here):

Wish me luck!

Edited April 17, 2021 by JapanAxe
Image linking problems

[Chienmortbb]

Although I am a Solid state amp man, I will follow with  great interest.

Edited April 17, 2021 by Chienmortbb

[Hellzero]

I wish you all the luck @JapanAxe and will follow this thread with interest.

[Beer of the Bass]

Sounds promising! Are those Hammond chassis made from steel? I very much recommend buying a chassis punch to make the holes for the valve bases, as that will be hard to do cleanly with a drill. Fortunately you only need one size when all the valves are octal bases.

[JapanAxe]

4 minutes ago, Beer of the Bass said:

Sounds promising! Are those Hammond chassis made from steel? I very much recommend buying a chassis punch to make the holes for the valve bases, as that will be hard to do cleanly with a drill. Fortunately you only need one size when all the valves are octal bases.

Yes it’s 20-gauge steel. I have a couple of chassis punches but I will get another one to suit the octal sockets.

One challenge will be cutting a rectangular hole for the IEC mains inlet. Does anyone know where I can get one that’s designed to fit a circular hole e.g. to replace a Bulgin connector?

[nilebodgers]

4 minutes ago, JapanAxe said:

Yes it’s 20-gauge steel. I have a couple of chassis punches but I will get another one to suit the octal sockets.

One challenge will be cutting a rectangular hole for the IEC mains inlet. Does anyone know where I can get one that’s designed to fit a circular hole e.g. to replace a Bulgin connector?

Why not do a powercon? Standard d-style Xlr hole.

[Beer of the Bass]

7 minutes ago, JapanAxe said:

Yes it’s 20-gauge steel. I have a couple of chassis punches but I will get another one to suit the octal sockets.

One challenge will be cutting a rectangular hole for the IEC mains inlet. Does anyone know where I can get one that’s designed to fit a circular hole e.g. to replace a Bulgin connector?

I replaced the Bulgin mains connector on my old Hohner Pianet with this style of IEC socket. I think it's not truly intended for a round hole, but covers it more effectively than the standard IEC sockets with the holes on either end would.

https://uk.rs-online.com/web/p/iec-connectors/2378894/

[Jus Lukin]

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Edited March 14, 2022 by Jus Lukin

[Chienmortbb]

3 hours ago, nilebodgers said:

Why not do a powercon? Standard d-style Xlr hole.

I have a 25mm Q max cutter you can borrow if you decide to go the PowerCon route. 

[SpondonBassed]

Great topic.  Good luck with the build.

[JapanAxe]

6 hours ago, nilebodgers said:

Why not do a powercon? Standard d-style Xlr hole.

 

6 hours ago, Beer of the Bass said:

I replaced the Bulgin mains connector on my old Hohner Pianet with this style of IEC socket. I think it's not truly intended for a round hole, but covers it more effectively than the standard IEC sockets with the holes on either end would.

https://uk.rs-online.com/web/p/iec-connectors/2378894/

Out of the two I think I will go the PowerCon route. I don't normally use odd connectors for gigging kit, as I like to carry spares, but this will be home use only.

3 hours ago, Chienmortbb said:

I have a 25mm Q max cutter you can borrow if you decide to go the PowerCon route. 

Thanks, that's uncommonly kind, but I will just get one myself - I rarely pass up the opportunity to acquire a new tool!

 

Thanks for all the other encouraging comments too.

[Passinwind]

On 17/04/2021 at 03:34, JapanAxe said:

Over the last few years I have had reasonable success building a handful of small valve amps. I do miss the Ampeg PF-50T that I sold on to purchase an EBS, so the time is right to start possibly my most ambitious scratch build yet. I previously enquired in this thread as to what version of B15 to go for, and I have settled on something close to a single-channel version of the Heritage model (i.e. switchable between 25W cathode bias and 30W grid bias), working from the Ceriatone 'Aunt Peg' layout.

Most of my previous builds have leant heavily on recycling old parts, but this time I am going for quality new parts. I have neither skills nor tools to tackle woodwork, so I am going for a Hammond 'birdcage' style housing. When assembled it is about 12in wide x 10in deep x 7in tall. The transformers (on order from Primary Windings) and valves will all stand up within the mesh cage (proportions not the same as shown here):

Wish me luck!

Salut, and best of luck. I've been taking a break before finishing up the 100 watt one I started last year but it's very close to finished and now that the weather's nice I can finally finish up the last of the metal and woodwork. Here's the general idea:

 

 

 

Edited April 18, 2021 by Passinwind

[JapanAxe]

17 hours ago, Passinwind said:

Salut, and best of luck. I've been taking a break before finishing up the 100 watt one I started last year but it's very close to finished and now that the weather's nice I can finally finish up the last of the metal and woodwork. Here's the general idea:

 

 

 

That looks pretty monstrous @Passinwind!

I've just finished ordering nearly all the parts for my build. There may well be a few more bits of hardware to get later (e.g. bolts for the rubber feet) but I'm pretty much there. I've taken the opportunity to buy in spares along the way, including replenishing my stocks of 600V hookup wire. Even allowing for that, my expenditure has already exceeded what I paid for my PF-50T brand new (admittedly on an end-of-line blowout) but much less than a Trinity TripTop kit would have cost - let alone what you would pay for an actual B15!

I've gone for some tested NOS Sylvania 6SL7GT valves in the preamp, and a pair of Shuguang coke bottle 6L6GC for the power amp. I already have a JJ GZ34 rectifier.

[Beer of the Bass]

The cost factor is what has discouraged me from doing something similar. I enjoy building amps, but the PF-50T basically ticks all the boxes for what I want from a valve amp for bass, and I would have struggled to build a well-presented amp with new parts and similar functionality for the price they were at on the Kenny's deal.

[JapanAxe]

15 minutes ago, Beer of the Bass said:

The cost factor is what has discouraged me from doing something similar. I enjoy building amps, but the PF-50T basically ticks all the boxes for what I want from a valve amp for bass, and I would have struggled to build a well-presented amp with new parts and similar functionality for the price they were at on the Kenny's deal.

Yeah I enjoyed my PF-50T, particularly the way the sound got ‘furry’ with the wick turned up. I wasn’t keen on the form factor though - I always felt like I had to baby it to avoid damage to the gubbins on the top, and the lack of a handle made it a two-handed carry from case to cab.

Iirc disssa of this parish commented on his web page that the PF-20T sounds closer to a B15 than the 50 does, although I have never seen schematics online for either of the modern units to enable a circuit comparison.

I think the black-painted Hammond enclosure will give me a fighting chance of producing a good-looking head. If I do pink torpedo things up it would probably be quite costly, but hey, not my first rodeo.

Once completed I plan to use the amp with my Barefaced One 10 - that’s got to be a perfect marriage!

[Geek99]

How much does it actually cost to build a valve amp from a kit? I own a soldering iron and a multi meter 

[Beer of the Bass]

I did put a B15N derived 6SL7 preamp in a Dynacord head I had, though that was with a very clean running power amp with high plate voltage and a lot of negative feedback, so the feel of the amp was probably a little different.

I get the impression the inductor midrange circuit on the PF-50T has a particular sound, especially when boosted, that may move it away from sounding like a B15N and more towards the V4 and other Ampegs. I haven't seen inside the PF-20T to see how they did the mid control, but maybe that's where some of the difference is.

[Jus Lukin]

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Edited March 14, 2022 by Jus Lukin

[JapanAxe]

28 minutes ago, Geek99 said:

How much does it actually cost to build a valve amp from a kit? I own a soldering iron and a multi meter 

Like many people I started with a 5E3 Tweed Deluxe. Mine came from Modulus - this page gives you prices and options. There’s also Ampmaker who does a range of low-power amp kits and apparently gives excellent build support.

If you are new to building I recommend starting with one or two pedal kits from Fuzzdog or Jed’s Peds.

WARNING 1: Valve amps contain lethal voltages which can remain long after the amp is switched off. Any builder needs to educate themself as to the dangers and how to minimise them.

WARNING 2: Amp building is highly addictive and can seriously harm your wallet!

[Geek99]

Oh dear - not for me then 

[JapanAxe]

12 minutes ago, Geek99 said:

Oh dear - not for me then 

🤣  On which count!?

[Passinwind]

3 hours ago, JapanAxe said:

That looks pretty monstrous @Passinwind!

I've just finished ordering nearly all the parts for my build. There may well be a few more bits of hardware to get later (e.g. bolts for the rubber feet) but I'm pretty much there. I've taken the opportunity to buy in spares along the way, including replenishing my stocks of 600V hookup wire. Even allowing for that, my expenditure has already exceeded what I paid for my PF-50T brand new (admittedly on an end-of-line blowout) but much less than a Trinity TripTop kit would have cost - let alone what you would pay for an actual B15!

I've gone for some tested NOS Sylvania 6SL7GT valves in the preamp, and a pair of Shuguang coke bottle 6L6GC for the power amp. I already have a JJ GZ34 rectifier.

Cool, I considered the Trip Top route myself but I already had a lot of parts stockpiled for my new build so my recent outlay wasn't as stiff as it might have been. I'm using an NOS commercial tube power amp board that came with a stout power transformer, and a set of leftover preamp boards from a rare commission build I did for a friend back in 2013. The case is semi-custom work and the maker only charged me $20 for a subtantial amount of CNC machining. A luthier friend laser etched half a dozen different fascia panels for the front, the one in the pic was just the first of those. For starters the tube complement will be one 12SL7GT (these are much cheaper and more plentiful than NOS 6SL7GT over here), two 12AU7s, and four TAD EL34Bs, with a Partridge/Hiwatt DR103 output transformer clone from Heyboer. I was able to borrow back one of my old rack preamp builds from the current owner and while I was doing a set of mods for him I had plenty of opportunity to hear how that dovetailed with the new power amp section.

I have had really good results with old JAN Sylvania 6SLs, which tend to go for ~$30-50 a pop these days from my usual sources. For less than thirty bucks I got all this and more by going with 12SL7s and a couple of 12SN7s:

 

 

 

 

Edited April 19, 2021 by Passinwind
insufficiently caffeinated

[JapanAxe]

4 minutes ago, Passinwind said:

Cool, I considered the Trip Top route myself but I already had a lot of parts stockpiled for my new build so my recent outlay wasn't as stiff as it might have been. I'm using an NOS commercial tube power amp board that came with a stout power transformer, and a set of leftover preamp boards from a rare commission build I did for a friend back in 2013. The case is semi-custom work and the maker only charged me $20 for a subtantial amount of CNC machining. A luthier friend laser etched half a dozen different fascia panels for the front, the one in the pic was just the first of those. For starters the tube complement will be one 12SL7GT (these are much cheaper and more plentiful than NOS 6SL7GT over here), two 12AU7s, and four TAD EL34Bs, with a Partridge/Hiwatt DR103 output transformer clone from Heyboer. I was able to borrow back one of my old rack preamp builds from the current owner and while I was doing a set of mods for him I had plenty of opportunity to hear how that dovetailed with the new power amp section.

I have had really good results with old JAN Sylvania 6SLs, which tend to go for ~$30-50 a pop these days from my usual sources. For less than thirty bucks I got all this and more by going with 12SL7s and a couple of 12SN7s:

 

 

 

 

That's the way to do it!

My last build was a tweed Champ/Princeton in the carcass of a dead Line 6 Spider, so the cab and chassis were already sorted.

[Passinwind]

14 hours ago, JapanAxe said:

That's the way to do it!

My last build was a tweed Champ/Princeton in the carcass of a dead Line 6 Spider, so the cab and chassis were already sorted.

I've done many builds using repurposed parts like that, especially for guitar. But over the last few years I've really come to enjoy doing my own circuit board layouts with my own design tweaks, and getting CNC work done in general has become pretty easy and highly addictive!

Edited April 20, 2021 by Passinwind

[Geek99]

8 hours ago, JapanAxe said:

That's the way to do it!

My last build was a tweed Champ/Princeton in the carcass of a dead Line 6 Spider, so the cab and chassis were already sorted.

So I looked at ampmaker. Some of these  amps are kicking out a colossal 18w. How loud are they in reality? I assume you can’t just plug headphones in to the speakerOut socket 

further, they call them guitar amps but I assume they can handle bass ?

Edited April 19, 2021 by Geek99