Re-starting amp-building after 10 years... What to build?

[vanslycken]

Hi everybody,
long time no see... I didn't even know the forums had changed. tboy is still in charge I see. Is Steve Ahola still around? He's the only one I remember from those days.
I got interested in tube amps when I was younger, I wanted to build some kind of Marshall clone when I was 18, but due to circumstances the project got tossed aside. Finally I found the time to restart it - well, dust off all the stuff. I found I had forgotten quite some stuff about tube amps. I started rereading the Weber books and some other literature, but meanwhile maybe some of you guys have the time and want to brainstorm a little as to what to build.

Here's what I already have:
- A 4x12" cabinet (homemade) with low-cost guitar speakers (monacor brand) which are rated 100W each. A second cabinet is waiting to have speakers installed.
- I have a power transformer giving 320-340-360VAC, a 40V winding for bias circuitry, and a filament winding powerful enough for 4xEL34 and some preamp tubes.
- an OT for marshall style amps (100W)
- a reverb tank (accutronics, I will post the type when the boxes are unpacked)
- 4xEL34, some 6L6s (actually spares for my Fender amps but I wouldn't mind ordering some extra) and a bunch of 12AX7s and of course all the passive components that are needed.

My original idea (when I was 17) was to build a 6-channel amp loaded with knobs and switches. Now, I'd rather keep it simple and full of "tone". Maybe a 3-channel amp, I'd like a clean channel, a bluesy-to-hardrock-overdrive channel and maybe a full metal channel.
I'm also a fan of vibrato and reverb, I was thinking about a vibrato which is connected to the power amp (there are some Fender designs around, maybe someone can point me to those amps) so the vibrato is the same for all the channels, and a reverb circuit (maybe something like the praised fender stand-alone-unit).

Now, if you were me, what would you do? Some things I'm wondering about:
- Is there any use in making a "hybrid" power amp with a pair of 6L6s and a pair of EL34s, maybe with a separate "master volume" for both pairs? Or is this ridiculous or impossible?
- Can someone remind me what the good and bad points are about pentode or triode operation for the power amp?
- Is it possible to run 4 EL34s in class A or is that ridiculous or are there things that might blow up?
- For the sake of cost and simplicity, I'd like to use solid state rectifiers. Is a choke really necessary if the filter caps are big enough? Any other thoughts on this?
- Preamp circuitry: suggestions? Channel switching or blending or something like the d**ble or trainw*** (do you still have to censor these words nowadays?) which - if I remember well - are controlled by the guitar's volume?

So, those of you with some time on their hands, let your imagination run wild while I read up on all the theory I've forgotten... Thanks!

Oh, I forgot to mention the sound I'm looking for. I like classic rock a lot, today I was listening to A Simple Man (by Lynyrd Skynyrd), that's a great sound. As for the "metal" voicing, I'm a sucker for things like Maiden and Metallica and Deep Purple. Of course, I can't play the way those bands do and I never will. But I hope to come a bit closer soundwise ;-)

[daddario]

Hmm... For that metal channel maybe you should try a tube-based distortion. Something like here: http://www.webmedia.ee/~martinh/elek...lib/koviak.pdf
The 6Z4P should be a 6AU6 and the 6N2P should be something like a 12AX7, but you actually don't need it. It's only for the low-impendance output.

[imaradiostar]

Some thoughts...

it's extremely difficult to make one amp do a million things well and switch quietly and operate with no hum and so on and so forth. It's also difficult to make one design sound like another. At some point if you try to stuff too many designs into one box you've kinda missed the point of having different amps and different sounds- it gets too big and messy and difficult to be worth the effort.

Here is what I would do...

Assuming you've got the skills and knowledge to fab your own turret or eyelet boards and have a good grasp of grounding and such I think you should build a "dual preamp" three channel amp. I would avoid verb for simplicity's sake but that's just me.

I'd make the first preamp & channel a blackface fender style- lower the Ck on the input triode because this stage will also feed your high-gain preamp. I prefer to not use the 3m3/10pf conjunctive filter but that's because I think it makes most pedals sound like crap- if you like the bright spanky sound of a fender twin's verb channel then maybe you should try it- you'll need an extra triode here.

Preamp 2 channel 2 would use V1a from the "fender" channel above and feed a Soldano style "lead" channel. One this particular channel I would have the cold cathode (39k Rk) stage switched out to lower gain and use very master volume marshall kinds of values- 500pf 33k tone stack, switchable .68 uf Ck's, etc. My goal here would bluesy gain through thick medium gain (think bogner shiva or top hat emplexador, vintage marshall, some brown soundish stuff...you get the idea). Of course you'd have to use an LDR or relay here and there to make things happen. Extra points here for clean layout and excellent grounding.

Preamp 2 channel 3 would more or less be the same as above but with the cold cathode stage switched in- look at a mesa dual rect or 50 watt solo head for examples. If you want that characteristic Mesa grind you could try putting an LDR or relay in the power amp feedback loop like a Mesa red channel. Mostly based on a Soldano, this would be your heavy metal/crunchy rock channel.

Thus far you'll have used three dual triodes. Another one could serve as an effect loop send/return and an additional one could serve as a phase inverter of your choice. I tend to favor EL34's because of their high gain but 6L6's may achieve a better heavy tone and clean tone- something about them not "sweetening" the signal like the big pentode does. You could really screw with people and use a pair of 6550's for a different sound and power level. With your transformers the voltages might be a bit low to get big power out of 6550's.

I personally wouldn't bother with triode switching. If you're like most other people out there it'll never leave pentode mode after the first week or two.

I recently built an amp with an ultralinear output and while it doesn't sound like so many other guitar amps the control and ability to let individual tones shine through is pretty great- it doesn't blur the differences between guitars or effects like some more colored amps do. The bass response is also impressive for the low power of the amp. I'm looking forward to trying an ultralinear output on a high gain amp in the not-too-distant future.

dang it's late, why am I online?

jamie

[imaradiostar]

just re-read the initial post.

Maybe you should cut your teeth on something without channel switching- build a single-channel marshall circuit with an active effect loop and see how it goes.

my first couple amp projects were pretty messy and didn't work great without a multitude of channels or built in stuff to muck it up. It usually takes a few builds and some pulling of hair to get up to speed and get used to troubleshooting and making different parts play nice together. It sounds like you've got some good knowledge so I don't mean to talk down (I'm no expert by a long shot!) but don't set yourself up for frustration!

I can only recommend you pick a proven design and layout and build something you can enjoy. My rule is if I can't wire it up in one Saturday once the chassis is drilled and turret boards are made then it's too ambitious and it won't get done. While it's not always the case I've proven myself right on several occasions and have the abused amp chunks to prove it.

now I reeeeeally have to go to bed. It's 4 now!

jamie

[GibsonLover]

Hmm... For that metal channel maybe you should try a tube-based distortion. Something like here: http://www.webmedia.ee/~martinh/elek...lib/koviak.pdf
The 6Z4P should be a 6AU6 and the 6N2P should be something like a 12AX7, but you actually don't need it. It's only for the low-impendance output.

Sorry for the side track, but I haven't seen the Koviak in a long time.
Here's another schematic with a different data for those interested.

[daddario]

GibsonLover: Yes, on that site there is that schematic too, but there is said, that there are some errors on that version. I would give the link, but the text is in estonian, so no help there. Tho there is not much information anyway - most of the text is how the heater supply was made.

[vanslycken]

Thanks for the replies, I've been re-reading a lot; this isn't my first project and I know the usual problems that might come up.

For me, it's not about getting it done on one saturday... I've been giving it some thought and here's what I'm going to do:

- build a power amp with 4xEL34, like a "regular" marshall
- once i've got that sounding good (or at least working) with a normal line signal, build a blackface fender preamp as you suggest
- once that all sounds well, try a marshall style preamp
- once that's done, try to combine them and add effects like vibrato and reverb.

Thanks for your help, I was feeling a bit lost since I hadn't been designing tube circuitry for a long time and I didn't want to blindly copy some design...
Once I have "real" questions I'll post them, and when it's done I'll let you know. Might take a couple of months though :-)