Twincaster commissioning issues......

[son_of_a_didley]

Hi there folks, I would be very grateful if you would be able to get my twincaster up and running. First I should say that I have only built 4 pedals before. I have managed to debug all of these and get them running no problem ..... but I'm a complete novice when it comes to valves and I'm struggling to figure this one out. To describe the problem, I get a bypass signal fine but silence/ occasional very weak signal when engaged with all knobs at max. The valve heaters are powered and the valves have a soft glow. I've checked and double checked the orientation of the polarised capacitors. I've now built an audio probe to test the circuit. So I can test the signal path, would anyone be able to clarify the signal path through a 12au7 valve for me? As I understand it, pin1 links to pin6, pin 2 links to pin 7, pin 3 links to pin 8. Is this correct?

Many thanks,

[Vitrolin]

please post the schematic you used for your project or we might not be talking about the same components

[son_of_a_didley]

Thanks for the quick reply. I'm using renegadrians version.... http://www.aronnelson.com/gallery/main.php/v/Renegadrian/Twincaster+rev+0_11.jpg.html

I spent some time tracing with the audio probe (excellent tool!) and found my problem - cold solder on a capacitor! I'm delighted to have it running and it sounds great. The problem I'm facing now is noise when I stop playing. After about a second after the guitar fades out hum starts to build up.  There is a clear gap of about a second... then humming in rapid pulses. I'm using a cheap 12v 2A regulated adapter which I'm guessing may be the problem. Has anyone else had this issue? I know hum is expected with valvecaster type pedals but I wondered if the rapid hum pulsing was symptomatic of something?

[PRR]

Is the wiring neat and compact? This 2-stage amp has enough gain to squeal. It may be squealing at supersonic pitch- you don't hear it, but the extreme signal mis-biases the amp. When mis-biased enough, gain falls off, squeal stops. The mis-bias bleeds-off (often around a Second) then the squeal starts again. Look at classic tube amp guts and try to be even shorter/neater.

Is it in a box? An open board on the bench is bound to have troubles.

Try adding 100uFd to 1,000uFd 16V or greater from B+ to ground where power comes to the board. While less likely on a 2-stage build, sneak-back through a poorly filtered power rail can cause sub-sonic oscillation (squeal, but very-very baritone).

It should be possible to have "zero" hum with a circuit like this, if the power supply is very clean, the board is shielded, the tube is shielded, all in/out connections righteous. (And shielding the tube is very rarely essential for a usable hum level; most tube-amps lose their shields and nobody bothers. The internal plate is a fair shield. For test, wrap the tube in foil and jumper to chassis.)

[son_of_a_didley]

Thanks for the reply PPR. Well my wiring is tidy but perhaps a little too optimised. I've superglued most of the wires together to keep them in place, given that I haven't used shielded cable this may be the source of it. I wouldn't normally optimise so tightly but I've built this up inside an old cast iron fuse box and needed the wires out of reach of the switching mechanism........ I will replace the signal wires with grounded shielded cable and see how it goes. I'll post an update over the weekend.  Thanks again.

[son_of_a_didley]

Update:  Well what a difference shielded cable makes. The pedal is now up an running with no hum. It definitely gets a bit wobbly with both gains at max and being boosted by a compressor, but I seem to like it with one gain a 0 and the other at about 2 o'clock. It has a really thick sound which I wasn't expecting. It occasionally sounds a bit gated in the low end but I'm guessing this this normal right? If I can work out how to post a picture you can see it in all its cast iron glory. Thanks again for your help folks.

[son_of_a_didley]

Ok, hopefully this will work

https://flic.kr/p/AJ4Rj4

[SuzukiScottie]

Looks good!

[son_of_a_didley]

Thanks! I rigged it so that the lever switch powers the LEDs under the valve. It works with a satisfying clunk

[PRR]

> a satisfying clunk

It's been in the rain a while?



It was once a fuse-box. Glad it has found a new life.

--Oooops, I didn't catch the price. Clydesdale's was asking "6/6" postpaid for "unused but slightly marked externally due to being stacked". What did "6/6" mean; six pounds and change?

[stallik]

6/6 means 6 shillings and sixpence. From pre decimalisation when there were 12 pennies to the shilling and 20 shillings to the pound. I make that 35p currently or a little over 50 cents!

[son_of_a_didley]

No way! What an interesting find. I had no idea it was that old. It was found in the garage of my brothers house in Bristol and I was given it as he thought it would make a cool stomp box. The guts of it were a ceramic block with a single rewireable ceramic fuse leading to two switches. Unfortunately I needed to trim the ceramic block to make room for the circuit board, but at least the switch is still functional, if only for cosmetic purposes.

I tried the twincaster out at band practice last night, it took 10 mins to fully warm up but was impressed by the result. The closest sound I can describe it as is Angus Youngs tone on Back in Black.

[PRR]

Six shillings?! Wish I could go back and buy the lot.

> no idea it was that old.

The cast construction is a strong clue. Bent welded sheet replaced cast boxes for most applications a long time ago. I can well imagine the basic tooling goes back pre-War. Electric service gear has long product life; my 2012 GE breaker box is essentially identical to one I know installed 1972. Clydesdale appears to be an odds-and-ends dealer, which suggests this product was already being eased-out of mainstream electric work by newer products, possibly larger (more circuits) in light of increased electric use. And if 50 cents was the most they could ask, it may even have become obsolete for most electric work (but perhaps ideal as a sub-panel just to shut off a ham radio transmitter, hence fodder for Clydesdale's customers).

[tubegeek]

I pulled this switch/fuse box out of a dumpster, not realizing the best thing about it: the Edison sockets that fuses fit into are the same sockets light bulbs fit into.

So this is a primo candidate for a ballsy light bulb limiter. Either I can build it into this sturdy box or use the box for something else and build the light bulb limiter on the fuse/switch hardware that was inside.

Win either way!

[PRR]

> a ballsy light bulb limiter

Just two sockets?

My first house had four (plus a big'un for the stove). My garage has eight (most don't do anything).

You may find the sockets a little close for many lamps.

In any case, if you want incandescent bulbs, better buy them now. The curly-tail CFs really hurt the supply of incandescents. 60W A-shape is hard to find. 60W Globe you can find, but sure won't fit two in that holder. Now $3 "60W" LEDs in shapes from slim/cheap to big-decorative will make incandescents very special-order.

250W inkys will be around a little while. They make sense for like a residential garage where the running-cost will never approach the first-cost, and you just want a cheap lamp. LEDs are still struggling to get in the "250W equiv" zone at impulse-buy price. I got a LED fixture near that bright but it is $60, versus $4 for dumb old-skool lamp.

250W inky at least avoids burning down the house, but is a little big to protect a project smaller than a Champ.

[tubegeek]

Halogen bulbs seem to be hanging in there at my local big box stores... more-efficient-enough to be permitted still.