DIY amps

pinksoir · 06-05-2012 08:17PM #1

I'm looking at possibly buying an amp kit from Weber. I'm waiting to hear back how much postage is, but it's looking like a Deluxe Reverb clone is $465 for the head, including cab, tolex etc.

I recently sold my Supersonic 60 Combo (too loud for use in my home studio and I needed to buy other gear anyway) and I've been using Amplitube Fender for recording, but tbh it's so far away from realistic it's grim. So I'm gonna build an isolation box and I'm gonna convert my old Fender Deluxe 112 Plus combo (solid state and a piece of turd) into a 10" or 12" cab to go in it. Or I might just build an all in one isolation cab. Not sure yet.

My other option is to buy a second hand head like a Bassman, Bandmaster or Showman. Or else something like a Blues Junior or Hotrod Deluxe combo.

Has anyone built amps here? I've built a good few things (pedals, synth) and am pretty handy with the iron at this stage. I've had a look at the schems and layouts and it looks like something I could handle (I think). Would I be better off trying to find a second hand head or even buying a contemporary combo (Fender). I really love the Deluxe Reverb and I can't really afford one, and, besides, what I really want is a head. I will use it live, but for now it'll mostly be for recording using my isolation cab. I like the portability of a head too.

Any thoughts/advice/suggestions? Or tips you have from building your own amp?

TroutMask · 07-05-2012 11:33AM

I've done it. You'll need to be au fait with safety procedures and have a working knowledge of basic electronics. There are heart-stopping voltages in those amps. Seriously, you can die quite quickly :eek:

Weber will be expensive, as you'll have to pay 30% import duty on top of the price.

what I usually do now is pick a good candidate for restoration and rebuild it from the ground up. This means a recap of all electrolytics, replacement of all voltage delivery related resistors with metal oxide types, replacement of all signal resistors with either carbon or metal film (depends on sound), and replacement of all signal path and interstage caps with sonically superior products.

After this the valve sockets are cleaned and/or replaced and the valves added as necessary.

You'll need, at the very least, a good DVM (like a Fluke), and a scope & signal generator. The scope does not have to be fancy , but it's really hard to bias valve amps without one. You'll need a dummy load as well. If you want to add extra valve stages into the chassis, you'll need a set of Greenlee sheet metal punches.

Then the tweaks and mods begin

:D:D

pinksoir · 07-05-2012 12:28PM

Thanks. That's the thing that's putting me off, really. The aul dying. Scary.

I've had a look around the net for safety recommendations. Obviously never work on it when it's plugged in. Always allow the transformer to discharge.

Do you have any advice/tips?

Weber is alright. About €600 for a Deluxe Reverb head, inc shipping and import duty. Though I could buy a refurbed Silverface Bassman head for that. Or similar. No reverb or vibrato though.

pinksoir · 07-05-2012 01:16PM

Some amp safety stuff I've found online:

Amp Safety Tutorial

How To Drain Capacitors

TroutMask · 07-05-2012 02:23PM

There is some good and bad advice on those threads. The second thread's advice about draining caps, while technically correct, is too complicated - all you need is a regular 240V household bulb (incandescent) in a socket with tails, simply touch each tail to the ends of each of the large caps and the cap will discharge safely. Some people get more fancy and make a bulb or resistor discharger with probes and clips & all that: nicer to use but not really necessary. I made one using one of those low wattage 240 volt fridge bulbs years ago and it works perfectly. You'll get a nice flash as the cap discharges, then the glow will fade away and you're safe.

*NEVER* discharge a cap with no load (like a piece of wire or a screwdriver)
one of the contributors on your link said that he thinks this is cool, it's not (it's just dangerous and stupid). You don't need to discharge the small caps, and you don't need to discharge the transformer (in an audio amp, it cannot hold charge) - you only need to discharge the big caps.

Of course, one of the main risks comes from working on the amp when it's live, you'll have to do this when you bias, take measurements etc. You'll also need to wear safety glasses in case pieces of resistor start flying around.
Good luck with it and be careful.

pinksoir · 07-05-2012 03:29PM

Cheers. Yeah there seems to be a lot of contradicting opinions on the internet. When did this happen?

Good to err on the side of caution, though. Lightbulb idea is good, thanks for that.

When you mean the big caps, do you mean the ones in the filter board or the main board, or both?

Also, I'm looking at grounding options. Do you have any tips on that? Presumably all the jacks and pots need to be grounded. Should I run copper wire between the pots with another wire going from that to ground? Where would this ground be?

Thanks for the help.

TroutMask · 07-05-2012 04:38PM

pinksoir wrote: »

When you mean the big caps, do you mean the ones in the filter board or the main board, or both?

Not sure what you mean by this? The caps that hold (potentially dangerous) charge are the PSU filter/smoothing caps. These can be chassis mounted (as in a marshall), PCB mounted, or a mixture of both. They are physically large and connected to the rectifier valve or diode bridge. They typically have a value of 16uF - 50 uF and a rating of 350-500V. They are often 'multicell' which means that they have more than one electrolytic cap in the same can. So, a Marshall will have: 50 + 50 uF @ 500 VDC in a big blue can - and there will be more than one of them.

pinksoir wrote: »

Also, I'm looking at grounding options. Do you have any tips on that? Presumably all the jacks and pots need to be grounded. Should I run copper wire between the pots with another wire going from that to ground? Where would this ground be?

The ground architecture is displayed in the schematic and should not be deviated from unless it is unsafe in some way. Most valve amps use the chassis as ground; the chassis, in turn, is connected directly (and legally!) to the mains ground.

It is good practice to run an additional ground rail along the back of the pots, and to tie this rail to the chassis. Preamp hum screening cans should be tied to chassis as well, electronically as well as by the physical connection provided by the fasteners. Jack signal cold connectors should go to chassis, and the signal hots should also short to ground when not connected, i.e., when a jack is not inserted.

Might be an idea to buy a book on Valve amp building as there are numerous
other things to be aware of, e.g., the orientation of the transformers w.r.t. one another, biasing, common fault symptoms etc.

pinksoir · 07-05-2012 05:43PM

Cool. Ok, so the ones you're talking about are the ones I called the filter board caps or these dealies:

01Filter%20Cap%20Board.JPG.jpg

The amp I'm looking to build is a 6A14 (Princeton Reverb), so the filter cap board is mounted on top of (or underneath depending on orientation) the chassis in a metal casing. I presume this casing would need to be removed in order to get at them... But anyways, I'm getting ahead of myself!

Most of the grounding info I've found recommends star grounding, which, as I understand it from building my synth, is using the same ground point for all ground connections, with each section (input etc) having a local node. Basically, one point on the chassis for all grounds which is then grounded to the mains ground.

How do you mean "legally" grounded?

There's quite a lot of build diaries and info on the net which is pretty handy. I reckon I'll buy a book though. Any recommendations?

Thanks again.

pinksoir · 07-05-2012 07:08PM

There's a nice silverface Bassman on eBay right now. Chassis only. I'm thinking about the lack of reverb. I have an external spring reverb but what's the main difference between a built in and external unit?

Obviously there's the fact that it's feeding off a tube with the built in, but say if I were to run the amp into my desk and then use the effects send on that to apply the verb, would this be serviceable? It would be post-speaker though, obviously. Putting it before the amplifier would work too but could end up with distorted reverb (which can be cool depending).

I'm nearly convinced I'm gonna build an amp, but if I can get a head, or the makings of one, for much cheaper I might go with that option... for now.

TroutMask · 08-05-2012 08:33PM

pinksoir wrote: »

There's a nice silverface Bassman on eBay right now. Chassis only. I'm thinking about the lack of reverb. I have an external spring reverb but what's the main difference between a built in and external unit?

Obviously there's the fact that it's feeding off a tube with the built in, but say if I were to run the amp into my desk and then use the effects send on that to apply the verb, would this be serviceable? It would be post-speaker though, obviously. Putting it before the amplifier would work too but could end up with distorted reverb (which can be cool depending).

I'm nearly convinced I'm gonna build an amp, but if I can get a head, or the makings of one, for much cheaper I might go with that option... for now.

Internal reverb splits off signal after the 1st pre valve (usually) and then returns it before the driver/phase splitter stage. External reverb has a wet/dry
control, it blends the signal that way. The tank you use is important - most of the great reverb amps are/were 'voiced' by the amp designers, i.e., the circuitry was matched to the tank for optimum sound.

I dunno about sending amps into desks, sounds like a good way to start a fire + run up some very expensive transformer bills. Seriously, valve amp OP stages need to see the correct loud at all times. Send & return stuff?? - you'll need some buffers or matching signal traffos to get that working correctly. Sounds like a separate project.

And here's the book for you:

http://www.amazon.co.uk/How-Hot-Rod-Your-Fender/dp/0760338477/ref=sr_1_29?s=books&ie=UTF8&qid=1336509000&sr=1-29

Connavar · 08-05-2012 08:53PM

Im currently working on a kit from ampmaker.com

It would be a cheaper option than weber if you see one that tickles your fancy

The instructions are really good even if you have no knowledge of what you are doing(like myself)

pinksoir · 08-05-2012 10:35PM

@ troutmask

Cheers,

Nah I meant amp to desk as in mic up the cab and then use inserts on the desk to add reverb. I'd never plug a tube amp straight into a desk! :eek:

I dunno, I'm feeling pretty confident about building my own now anyways ater all my reading. Thanks for the link to the book, I'll take a look...

@ Connavar

Cheers. I did see ampmaker before, but none of the kits are available right now, plus he doesn't really have any I'd be interested in...

DIY amps

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