JapanAxe

Who owns the PA?

Preset buttons?

It didn't look like any of those! The amp part was about 1U or 1.5U tall, about 15in wide, mainly black. I'm now starting to doubt whether it was actually an Ampeg or a flip-top, but it definitely had style-based presets in addition to regular tone controls...

The bass player in my first country band (in which I was guitarist) had a solid state flip-top Ampeg. This was around 1991. It was quite a compact unit that was attached to the top of a 1x15 speaker cab. I seem to recall that it had preset EQ profiles (e.g. ‘Pop’) that could be selected by push buttons on the front panel. So far I have been unable to find this mystery amp by the power of Google - any ideas? Just curious!

I probably won't get the transformers for another week as they are being built to order. In the meantime I have been considering my options as regards the heater filaments. The Ceriatone layout follows the Heritage schematic in having the heater centre tap connected to ground. I would normally do this, or in the absence of a centre tap on the PT I create a virtual CT using 100R resistors between each side of the 6.3V AC supply and ground. Both the 1964 and 1968 schematic show a 100R Hum Balance ('humdinger') pot across the 6.3V, with the wiper (marked K) connected to the cathodes of the output valves, which will be at about 36V above ground at idle. As I understand it, elevated filament voltages are intended to distance the heaters from any noise in the circuit ground, and the pot allows any residual noise on the 6.3V lines to be cancelled out. With proper grounding there shouldn't be any noise, but I think I will compare connecting the heater CT to the cathodes or to ground to see which produces the lower noise floor. If neither approach is satisfactory, I can consider adding a hum balance pot. If anyone has personal experience of heater noise in the B15 circuit, please do share!

I have started on a full-size layout for this build. As per my plan, the Ceriatone Aunt Peg uses just one preamp channel but provides the choice between cathode biasing (models up to 1964) and grid biasing (1968 models onwards). I have blown up the board layout to match the 70mm width of the phenolic board. To fit both cathode bias and grid bias components I would need to split the board into two sections. The PT I have ordered doesn't have a dedicated grid bias tap, but I could use the bias supply circuit from one of the later models that runs off the full HT. Alternatively I may just stick with cathode bias - this would be the more 'vintage' option, I don't need 5 extra watts at home, there would be less to get wrong, and I could easily fit everything on a single board. I would have a few components spare but there will always be another build! I am also tweaking the circuit in other ways, for example I will have just one input socket with a 33k grid stopper and 1M grid leak resistor, and I will be using a multiple star ground scheme as advocated by Merlin Blencowe. I have the dimensions for the transformers but I don't yet know where the leads will exit, so I won't go too far with the layout until I am sure of this.

I’m impressed that your bass hit the deck on the 1!

5 across: viva 7 across: limen 1 down: pulchrisima Sorry, 45 years since I did Latin...

Yes you need 32in scale strings on a Mustang to accommodate the extra length for through-body stringing.

My first guess would be the filter capacitors in the power supply. Electrolytic capacitors degrade over time and start to behave more like resistors i.e. they dissipate heat, which a healthy capacitor will not do.

In my guitar rack I have a 1985 Squier Tele alongside a Palir Titan T-type that cost me 10 times as much. They are both lovely instruments and both get gigged according to my whim at the time. Whatever works for you, do it, and fup the rest.

I‘ve had a fair amount of practice at buying (and selling on) music gear, consequently I have a clear idea of what is likely to work for me. I also have pretty much all the stuff I want. I won’t claim to be GAS-free, but it doesn’t loom large in my thinking. After one particular purchase the initial euphoria was quickly replaced by buyer’s remorse. Fortunately the more I used the item the more I liked it, but did make me question the whole GAS-powered buying process. I’ve found a substitute in building my own kit, mainly valve amps. This is much more fulfilling and possibly cheaper but it does bring its own problems - I can’t easily sell on surplus builds, and I end up GASing after tools and test equipment!

6SL7s are a new venture for me. I’ve always built with 12A*7 preamp valves (tubes) before. The 6SL7s I’ve bought are guaranteed, and I am building a head rather than a combo this time so microphonics would be less likely to be an issue. The fact that they are octal valves is a major plus as it is much easier to make solder connections to the sockets!

I use a Scarlett 6i6 in my home studio setup. One of the reasons for choosing it was that it runs off a separate PSU. My previous interface was USB powered but it picked up noise from other devices on the USB bus.

All valves now acquired: 2x Sylvania 6SL7GT, JAN standard 2xShuguang 6L6GC, current production - test as well-matched on my Orange valve tester 1x JJ GZ34 Some other parts also delivered today!

I don't like PJ basses.

Bits and pieces have been arriving, including parts of the enclosure. Here are the loosely assembled chassis and cover shown next to my Demeter head for scale. There will be plenty of room to work inside the chassis, which is always nice!

18W can be massively loud for a valve guitar amp. I gig a 15W Matchless and it has never been ‘not loud enough’. As has often been discussed here, bass amps generally require a bit more. No you can’t just plug headphones into the speaker output. There are solutions involving a load box but it can become a bit pointless. Yes you can connect one of these heads to a bass cab of the appropriate impedance, and you may be able to optimise the amp for bass by changing some of the components e.g. coupling capacitors. Vyse Amps do a 120W bass amp kit. Both Vyse and Modulus do a Bassman kit.

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.

🤣 On which count!?

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!

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!

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.

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. 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.

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?