making a 36watter with less than $200

[fredy]

Hello, i have decided on my next build, a 36watter that is switchable to 18watts. The thing is, i do not have much money for this project as i will be going to uni soon (and i need this amp for then).

I have some old transistor radios and cd played i could get parts from. I have a power tranny from one but all it has writen on it is a serial code. How can i find out the voltage/current of each tap? and can i use it for a PP valve amp?

I am also thinking about making a pocket valve amp for fun. Could i use those little transformers you get in desk lamps and wallwarts. i assume you cant as they are designed for a different purpose but i am an absolute novice.

Thanks.

[Alexo]

Normally you can't use transformers found in solid state gear for tube gear, SS usually runs somewhere between 6 and 24 volts, while tubes usually need 300 volts or more.

You *might* still be able to put a project together for that budget, especially if you can find a broken old tube stereo or something... otherwise, you could probably buy Hammond transformers for what you'd need for around $100.

But for a first build, I strongly recommend a kit.

[fredy]

this is my second build, i started with a 5 watt kit from loverocker.
hmmm, old valve radios are pretty hard to come by round here. I could get one of ebay for £40 bit you never know what you are getting. are they any specific models i should look out for?

[fredy]

Do you know where i could get a schematic and layout for such an amp? i tried looking in the download ection but to no avail.

[Alexo]

The rule of thumb is replace like with like.

For instance, if you score a single-ended 6V6 phono amp, the best candidate to build it into is a single-ended 6V6 guitar amp, so if you want a 36 watter, you would want a 4xEL84 mono-amp. That sounds kind of unlikely to find, you could probably find a stereo EL84 amp with one pair per channel, the power transformer from such a unit would be equipped to power a 36 watt, but the output transformers would only be good up to 18.

But beggars can't be choosers, part of the fun sometimes is working with the limitations of your materials.

I hear you though, guys are always talking about these old consoles and stereos they can get for free and gut, I've had one instance of good luck in that regard after scouring enough yard sales that I thought my girlfriend's eyes were going to wind up in a permanent "rolled" position!

[fredy]

of course, you are right. But i am a marshall man who needs a cheap workhorse of an amp which can be carted through the streets of guildford form gig to gig, keeping up with a loud drummer, and be used at home (with an attenuator no doubt , blimmin neighbours).

I could get a pair of transformers from loverocker but that will cost me £100/$200 and then with the speakers as well, and the valves, turret board, pots etc. i have blown my buget big time. I guess i could go up to £300 but anymore and i could buy a second hand reissue. and thats no fun, well not compared to making it anyway. I will search ebay and see what i can find.

[dartanion]

Hit your local thrift stores, garage sales, electronics recyclers, etc. and look for old console TVs and stereos. You should be able to find stereo PP EL84 amps in a lot of those units. For the OT, you can parallel the 2 OTs for use with a mono 36watt output section. It's been done before.

[tarzanalog]

Hit your local thrift stores, garage sales, electronics recyclers, etc...

Yeah. A buddy of mine just got a fully functional Hammond M100 for $10 at the Salvation Army store. Works perfect after a few squirts of Hammond-Oil.

I told him that I'd give him his $10 back for the AO-35 reverb amp that's in it. That's known to be a good starting point for an 18 watter...

The Heathkit W-5M I just got for free from an E-waste event is going to be the donor for a "Heavy IIb" amp. There's lots of stuff out there... get lookin'!

[dartanion]

A certain builder who calls himself a Doctor of the alphabet pretty much ripped off the AO-35 for one of his amp "Designs".

[tarzanalog]

A certain builder who calls himself a Doctor of the alphabet pretty much ripped off the AO-35 for one of his amp "Designs".

Funny how that works.

Andy Marshall of THD was pretty up front about many parts of his THD Univalve amp being "taken" from designs originating in the 40s and 50s like the light bulb filament NR circuit, etc.

I like it better when that happens... tipping the tip to those that went before... than when someone tries to patent everything for their own gain.

[fredy]

anyone know of a schematic and layout for a switchable 18/36 watt? and what type of trannys do i need? i will ask around and see what i can get hold of.

thanks for the hel so far

[beerman]

Check Ceriatone.com for that 18/36 layout. His parts are quite cheap too...

[tarzanalog]

fredy,

The 36W I have is Nik's. (Ceriatone)

It's terrific and the only changes I've made to the amp are carbon comps for the plate resistors in the power section and a few cap values on the EF86 channel tone switch. It's a great layout. Very quiet. Even when it's nearly cranked! (I think the layout is actually Richie's BTW... "Plexi" on this forum.)

[Michael]

Hit your local thrift stores, garage sales, electronics recyclers, etc...

Yeah. A buddy of mine just got a fully functional Hammond M100 for $10 at the Salvation Army store. Works perfect after a few squirts of Hammond-Oil.

I told him that I'd give him his $10 back for the AO-35 reverb amp that's in it. That's known to be a good starting point for an 18 watter...

The Heathkit W-5M I just got for free from an E-waste event is going to be the donor for a "Heavy IIb" amp. There's lots of stuff out there... get lookin'!

Yep! In fact, if you have zero amp building skills, you can use the AO-35 as-is. A bit boomy, but freaking loud! Bought mine on eBay with a bunch of Hammond amps. Guy didn't know what he had, or maybe didn't care. Cost was maybe $15.

EDIT: $15 was by pure luck. These normally go for around $100. Keep a sharp eye out and snatch it up if you see one.

[martinw]

Hi Fredy,
You'll be lucky to find any old radios, organs or hifi gear that will be suitable. Over here in the UK there just aren't the numbers of old Hammonds and suchlike.
If you are really strapped and need a cheap giggable amp, there are 2 ways I'd go: firstly, try and find an old Carslbro 50 on Ebay. I've seen them go for under £200 for what is a great 50 watt EL34 amp.
Look at this bargain:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... &rd=1&rd=1
Or you could look for a Marshall JTM/JCM600 series head. They aren't anywhere near as popular as many oither Marshalls, and the head version doesn't suffer from the heat problems of the combo versions. It also has a bigger OT. The combos aren't too bad though, I fitted a small equipment fan to mine and it ran fine. The JTM30 is cheaper still and still just about giggable, and can be retrofitted with EL34's to make it a JTM60.
There are many other less popular valve amps on Ebay you could hunt down.
Secondly there are some real bargains around on new gear. PMT are doing an amazing deal on the Ashdown Fallen Angel valve range. Also I had a Vox Valvetronic AD50VT which I paid well under £200 for and it does some excellent sounds. Great little amp.

As for a homebuilt amp, I doubt you'd be able to put one together for less than £300, and probably more if you want a combo, or a tidier cabinet. It all adds up like you wouldn't believe. Our American friends seem to be blessed with junk shops full of valve gear (as well as a broader range of suppliers of new stuff), but the best I've seen are old radiograms. If you can find one, and it's a big if, you can make a decent amp from them.

I have a schematic I used for my 36W (with 18-36 variable control) that I can post if you're still interested. Transformers are fundamentally AC30 type, and not cheap. Think £100 the pair shipped.
Good luck!

[Phil_S]

Fredy, I've done 5 amps with used transformers. This is the place where you absolutely will save money with the potential for absolutely no sacrifice in quality. For example, I took the transformer set from an Arkay FL30 for a JTM 45 (sounds great). This was an eBay purchase for about $25 and the amp had the "right" tube compliment.

Another thing that will save you money is a used chassis. This can be problematic, in that you will need to learn how to close or reuse existing holes. I tend to look at this as a challenge and try to have some fun with it. Take a look at what I did with the chassis for the JTM45. http://tinyurl.com/32whmw Pay attention to all the holes that I closed up on the front and back. Also, the turret board is in there crooked as a compromise because I elected to use certain existing holes for tubes. Notice that this was a rare instance for me where I elected to use the more expensive can cap. I felt there was not enough space inside the amp to comfortably use run of the mill axial or radial lead caps. This is also a place to save money. I've been buying inexpensive caps from the grill man.

I'd also mention, that terminal strips tend to be much cheaper than a turret board, however, you can usually get a decent turret board for under $30. This is one place I would probably spend the money, as it makes the task much simpler, quicker, and facilitates trouble shooting.

I think I spent about $250-300 in the end on the JTM45. I think you can do a 36W for $200.

One possible source of used transformers is www.oldradioparts.com. Finding a PT is likely there, but an OT is much harder to come by. Also, if you are very patient with eBay, my favorite search is "(amp, amplifier) (parts, project, chassis)" which turns up all kinds of interesting stuff. It can take weeks on eBay to locate something for a favorable price and you should 1) be careful about what you bid on, and 2) set limits, like $25, so you won't groan too loudly when you get burned.

It is important to understand what PT will work and what won't. After you come to some idea of what range of HT voltage (like 275-0-275) or whatever, you'll need to satisfy yourself that the PT has adequate mA capacity. To do this look at the EL84 spec sheet. You will be working with Ia Max in the range of 70-90mA per pair. To that you will need to add the little bits that the preamp tubes draw. That would make your minimum requirement at least 150ma and I would go with 200mA to be safe. You will get better performance (tone) from an amp that has an adequate power supply. If there is constant sag because the PT can't keep up, the PT will run hot (physically) and this couldn't be a good thing.

In the end, patience it the thing that will keep your cost down. The moment you get ants in your pants, the cost goes up. Also, be prepared to get burned a little in the process, as there is typically no recourse with used parts.

[fredy]

I found a guy in my town who restores valve amps, he may be able to help me with the transformers hopefully.

i have been looking on the ceriatone site for a layout. is the one with downscaling? i assume thats what the half/full switch does.
http://www.ceriatone.com/images/layoutP ... iatone.jpg

From that layout it seems i will need a tranny that produces 290 B+ (or is it 580? i always get confused with this, i think its the later but not sure) and 3.15v (6.3 (must be the later, 3.15 is far too small)) for the heaters. with my understanding of transformers, current AND voltage can not be defined at any value as if you cahnge one you change the other so the values for voltage above should mean that no matter what transformer i have, as long as it has the correct voltage, the current will also be fine. does that make sense?
anyway, how much can i stray from these values?


the layout on the web site doesn't show the values of the OT, what will these be. I know the secondary will need to be 8 and 16 (i want to be able to switch from 1 and 2 speakers when necesary)

thanks.
thanks.

[dartanion]

PT should be 290 - 0 - 290, 200mA and 6.3V at 4A and 5V at 2A minimum.

OT should have a primary Z of around 4k ohms.

[martinw]

Blimey Fredy, not trying to be funny, but wouldn't you be better off with a kit?

[fredy]

thats no fun and the onyl british kits i know of are ampmaker (out of action for a while) and that other one (overpriced) i wouldnt mind a metro jtm45 though, but that will replace my TSL and will stay at home as it worth too much, especially with inporting it here.