Anyone with experience building valve amps?

[GREEN FUZ]

As a first foray into amp building I want to make a small practice amp. I`ve got an old radio chassis which will serve as the housing, so this will dictate the overall size. I`m not averse to going the solid state route but quite fancy the idea of a small valve amp. I`m thinking something along the lines of a Fender Champ. Maximum 5w more than likely. Decent clean sound to mild crunch. Volume, gain and tone should be enough (maybe too much). Can anyone suggest a viable starter build for someone with absolutely no experience in this field?

I`ve had a look at the usual sites like www.ax84.com but any alternatives are welcome

[v846]

Try here



http://angela.com/simple6v6guitaramplifierproject.aspx



David

[Paul Marossy]

I still like the Octal Fatness a lot.

[doitle]

I had a similar plan. Just picked this up the other day for 5$



Zenith Y832 Tube Radio

I need to learn some more though before I can get this all figured out. It doesn't work in it's current state. I've read that I need to replace all the caps likely before it will work again and also will probably have to replace the tubes if they are bad as well. Been a little busy though lately.

[sean k]

There are some articles out there by Norman H crowhurst and they make the job of understanding tubes reasonably easy.

Single ended, or class A is easy on parts count but output trannies are expensive when they're good for the job. Class AB or push/pull amps have a few more parts but they're more efficient and are the bulk of guitar amps out there.

Tube construction is more hands on than this stompbox stuff and I love all the bending and filing usually required to build the chassis and wooden boxes that they sit in... proprietarly.

The 6BM8's and 6GL8's (I think) are a voltage amp triode and an output pentode in one package, of about five watts in p/p and two of those with a 12AX7 and a coupla hammond transformers is a simple straightforward startup amp. Read crowhurst and design your own!

[petemoore]

  Before spending on caps, consider there's probably no isolation tranny for the AC input, in which case the hot chassis design makes a workaround..compete with the idea of redesigning or picking a design which has a 3rd prong which connects the chassis and you to ground instead of a hot wire.

[mnordbye]

Don't know if you live in Europe, but i've heard good things about these kits: http://www.musikding.de/product_info.php/info/p795_Kit-Madamp-G2.html

If not, AX84.com was my introduction to building tube amps. Great stuff!

[sean k]

You've so got to keep the cabinet for that Zenith and made the tuning knob and its dial your master volume. That Baby, no matter how many watts you make it, has to go up to at least 14 and a half... maybe even 14 and three quarters.

[doitle]

It actually has a switch on the back to switch between radio mode and phono input mode. I'm planning to just add a preamp stage to that phono path and otherwise keeping her stock. I hope to have a fully functional olde timey radio and nice little Class A tube guitar amp.

[GREEN FUZ]

From what I`ve read, while it can be done, straightforward conversion of radio`s for guitar use is far from ideal. My intention is to gut the enclosure and use it to house the guitar amp circuitry. That first link is pretty much the sort of thing I had in mind, thanks David.

Any tips on disembowelling the radio without doing myself some damage? I was hoping to adapt the original chassis and if possible some of the components in order to minimise any further tooling. The model I`m working with is actually a "portable" battery type, so no mains.

Here`s a link if anyone is interested.

http://www.vintageradio.me.uk/workshop/workshopdsqueen.htm

Thanks to all who took the time to answer.

[g.]

you can use a 6BM8 SE (ecl82) as Sean k said

it's a tube with one triode and one pentode in the same enclosure
i've made an hifi amp with these
very good sounding tubes

here a schem for guitar amp (really simple)


http://www.freewebs.com/niteglow/

[Derringer]

From what I`ve read, while it can be done, straightforward conversion of radio`s for guitar use is far from ideal. My intention is to gut the enclosure and use it to house the guitar amp circuitry. That first link is pretty much the sort of thing I had in mind, thanks David.

Any tips on disembowelling the radio without doing myself some damage? I was hoping to adapt the original chassis and if possible some of the components in order to minimise any further tooling. The model I`m working with is actually a "portable" battery type, so no mains.

Here`s a link if anyone is interested.

http://www.vintageradio.me.uk/workshop/workshopdsqueen.htm

Thanks to all who took the time to answer.

as for gutting the existing radio ...
1. make sure it's unplugged
2. make a grounding strap and discharge any electrolytic that you see .... basically, connect the + side of all electrolytics to ground through a 100K/2W resistor ... each will discharge in a few seconds
3. then go at it with a pair of nippers/pliers

what does it look like inside? point to point with terminal strips?

[petemoore]

  Once you get a grounded chassis [3rd prong of AC plug connected], you are not committed to un-safety, also called ''2prong death trap''.
  Many of these devices were intended to NoT be connected to other equipment or humans.
  That simple amp looks fine. Some of the best sounds I get come out of little simple amps, much like that...1 preamp 1 output tube, nothing fancy, and make excellent pallete for stompboxes boosting/distorting etc. Nice wide frequency response, ability to distort at low volumes, generally sounding 'nimble'.
  When built right [ground scheme and power supply] the low noise and general ability to do 'tube amp stuff' makes them my go-to amps when I want no high volume levels, too big an amp for the room, IME, sounds 'big 'n clumsy', not as well behaved or fun.
 
 

[GREEN FUZ]

what does it look like inside? point to point with terminal strips?

This isn`t mine but an identical model. Bit of a mess.



I`m thinking the chassis can be reused.

[g.]

and keep that big air capacitor to make a tube wah !!

[petemoore]

  The left end of the amp [as shown in pics] looks to have 'radio stuff' which can be removed, opening up room for putting amplifier components on/in.

[Derringer]

and keep that big air capacitor to make a tube wah !!

heheh


yeah dude, I'd just make that cap-discharge/grounding strap like I said before (make sure it's grounded to earth), touch every + cap lead in there and hold for a few seconds, and then just start tearing things out. It doesn't look like there are any parts in there that you'd really want to salvage ... aside form the mojo-layden air cap

Like you said, just re-use the chassis and scrap everything else

I have a big old Halicrafters radio that I plan on doing the very same thing to someday ... except it will hold a 50 - 100watt valve head

[Derringer]

here a schem for guitar amp (really simple)


http://www.freewebs.com/niteglow/

What are the Transformers used here?

[doitle]

Shouldn't the input transformer still be usable? It is supplying B+ and the heater voltage for the tubes currently in there so it must be fairly useful.

[sean k]

Follow the link to the site for the nite glow and theres a description of the transformers used in... circuit description.
You guys in the states would have to go for different transformers to get the same turns ratio but its not impossible. I'm sure someone out the will have 120/4V transformer. I've got a bunch of old radios that used the 6BM8 and the 6GW8 (it wasn't an L) that are all single ended and have tiny little output trannies so I should do one of these myself.