noob jump start...

[Tonegeek]

Just joined. Been reading this fascinating forum all day at the peril of being fired - can't...stop...must build Dum...doh!!

I need to settle a few questions before I jump in and start building an amp.

1) This is the biggy, not really a build question:
I have a perfectly good 1970 Twin that I highly modded years ago for global verb, channel switching, high gain channel, etc. This amp has parallel channels instead of the serial arrangement of most Dumbles. I love the clean channel of this amp, but not the OD channel. Also, it is too damn loud for 99% of my needs. 50 watts would more than do. On the plus side it is paid for. basically, should I sell this amp, mod it or start from scratch? I am not using the amp. My skill level is not a factor (he says as the smoke rises from the bench...).

Ok on to more practical stuff...
2) should I use el34 or 6l6 tubes? (6v6's are interesting but afraid 2 of them is not enough headroom for the clean volume I need). I like Robben Fords sound across the board, lead tones, cleans, not a bad tone to be found. Would like to use whatever he is using on the output, however I play a Strat w ceramic based single coils PUPS, so that probably needs to be factored in. We can get to the tone shaping later, unless someone has a strong opinion on getting Dumbles to help a Strat sound fatter. Eric Johnson is the best example I can think of for that super fat sound from a Strat that I crave, so I know it is possible.
For some weird reason, I keep trying to get humbucker like sounds out of my Strat (any Strat players identify with that?) Still want to cover SRV though, so maybe I am asking too much. Ok, I know, I should get a Gibson, but then I wouldnt have the cash to build a Dclone...

3) Where can I get enough wire in the appropriate colors but without buying enough to circle the earth twice? I just want to build one amp for now so I dont need the 100ft rolls. Any of you guys got some extra I can purchase?
4) Is it OK to derive relay PWR off heater supply with a doubler or better to use a separate tranny?
5) Caps: Looks like ceramic is preferred here for pf values, but I have seen a lot of other amp modders replace ceramics with silver mica for the pf values. Gary gave me some good advice on many of the cap types already, but just need to settle the pf cap type.
6) It may help to have a drilling template if question 1 is "build from scratch". I am also open to buying a chassis kit, but am afraid that it may lock me in to some things I don't need, like the "rock/jazz" switch. I am building this amp for me, so even if it is from scratch, I will probably put my own touches on it. One thing about using the Twin, is that it has plenty of room to try different options.

Thats it for now. I am really getting excited about this project!
Whit

[Bob-I]

Just joined. Been reading this fascinating forum all day at the peril of being fired - can't...stop...must build Dum...doh!!

I know the feeling.... I have 5 now.

1) This is the biggy, not really a build question:
I have a perfectly good 1970 Twin that I highly modded years ago for global verb, channel switching, high gain channel, etc. This amp has parallel channels instead of the serial arrangement of most Dumbles. I love the clean channel of this amp, but not the OD channel. Also, it is too damn loud for 99% of my needs. 50 watts would more than do. On the plus side it is paid for. basically, should I sell this amp, mod it or start from scratch? I am not using the amp. My skill level is not a factor (he says as the smoke rises from the bench...).

Your choice really. You'd pretty much have to gut the amp. At this point the amp can be returned to a stock Twin and sold as vintage, once you make it a Dumble the value will most likely go down, but it will become useful.

I'm a fan of finding an old dead amp that can be converted. I converted a Fender tube PA head for a friend, a Peavey VTX combo and some others that are converted but not to Dumble's. Try searching in local stores for tube amps that a fried but have decent iron, or search ebay for "as-is" "Project" "Chassis" "needed repair" etc.

Ok on to more practical stuff...
2) should I use el34 or 6l6 tubes? (6v6's are interesting but afraid 2 of them is not enough headroom for the clean volume I need).

Robbin Ford and Eric Johnson are 2 distinctly different tones. Robbin is 6L6 100 watt Dumble where EJ is 50 watt EL-34 Marshall.

I like 6L6's and I've built both. If you get the right xformers you can make it switchable. You need the 4-8-16 impedance taps so you can match the tubes. Personally I like 50 watters using 6L6's and 20 watters using 6V6's but you're right about the lack of overhead. You might want to make a 4x6L6 and include a 50 watt switch.

3) Where can I get enough wire in the appropriate colors but without buying enough to circle the earth twice?

ApexJr sells by the foot. http://www.apexjr.com

4) Is it OK to derive relay PWR off heater supply with a doubler or better to use a separate tranny?

I have one amp that uses this, it's fine. No doubler, I used 6V relays.

5) Caps: Looks like ceramic is preferred here for pf values, but I have seen a lot of other amp modders replace ceramics with silver mica for the pf values. Gary gave me some good advice on many of the cap types already, but just need to settle the pf cap type.

Ceramic. There's a grainyness to the sound of these cheepys that silver mica will not produce.

6) It may help to have a drilling template if question 1 is "build from scratch".

If you like the Twin chassis, why not buy one. You could make your own faceplate. Search ebay, or go to http://mojotone.com or http://tedweber.com for chassis and cabinet.


Best of luck. Check out Normster's $300 Dumble project. With a better chassis, a bigger xformer set and relays you could scale it up to a full blown Dumble for pretty reasonable money.

Bob

[Icetech]

My $.02 which is really only worth like .01.. anyway.. if you own it and its paid for.. gut it and run it:) If it was stock or near stock and you wanted to sell then i would say different.. but modded already.. hell go all the way:)

Most of my stuff is built in fender chassis, i get rid of that fiberboard they used and use the generic turret boards from turretboards.com you get like 30 turrets per side... easy to work on and looks clean:)


Just this week i tried el34's in mine and kinda like em better.. seemed warmer to me, but my ears suck.. so to each their own..

And Bob, i know what you mean bout the single coils.. i got a nice shiny strat and couldn't take the SC sound... put a pair of HC's in and i have the nice big scale and feel of the fender.. but with tone:) and cheap...

[Tonegeek]

You might want to make a 4x6L6 and include a 50 watt switch.

Bob,
I tried this once on the aforementioned Twin (switch lifted cathodes from ground on 2 tubes) and in the 50w mode it took the life out of the sound. Is this where I need a multi-tap xfrmer so I can switch the speaker Z when I go to the 50w mode? Maybe thats why my sound was so dead. I am leaning toward Dumbleizing the Twin, but really don't want to sacrifice any tone in the 50w setting. I just really want the best sound I can get at 50 watts and if I can do it with the 100w Twin xfrms then I will, but if not then I will probably buy a chassis and build it for 50 watts. What's the consensus around here on the sound of a 100 watt amp switched to 50 watts?

Either way, I will set it up to use either EL-34 or 6L6. This seems to be mainly an issue of having enough variation in the bias voltage to accomodate either tube set.

Check out Normster's $300 Dumble project. With a better chassis, a bigger xformer set and relays you could scale it up to a full blown Dumble for pretty reasonable money.

What a work of art! Who needs a schematic with that layout!

[Luthierwnc]

I would find a new home for that amp and work from one of the BOM lists on this forum. Without more control over your Z-out, you need to start making compromises you might regret. Two tubes is usually enough. 50 watts out of one of these things is enough to leave skid marks. That and a Twin weighs a ton. A head, a cab and two trips to the car seems more reasonable these days.

The exception to this scenario is if you need to replace the speakers anyway. A two 6L6 version into parallel 16 ohm speakers gets the Z back on track but takes away from the economy of the existing parts. A lot of the recommended speakers for this project are available in 8 or 16 ohm models.

There are a couple vendors on eBay who sell 10ish foot lengths of 5 to 10 colors of teflon wire pretty cheap. If you really don't care what the colors are, one hank is enough to build a whole amp.

No matter what happens, the "must make Dumble" gods will be obeyed (I have two).

Skip

[Tonegeek]

50 watts out of one of these things is enough to leave skid marks.

The gigs I do and the type of distortion I like (pushing the power section a bit) make a 50 watter more practical

a Twin weighs a ton. A head, a cab and two trips to the car seems more reasonable these days.

I have been thinking for a while I should go to a head/cab arrangement, as my ageing back is wanting a break from hauling combo's around. Plus you have that cab to reuse on other amp projects.

A two 6L6 version into parallel 16 ohm speakers gets the Z back on track

If I interpret this correctly, if you switch off 2 tubes, then you need to double the impedance the Twin's 4 ohm output is seeing (2 16ohm spkrs in parallel = 8 ohms) probably the reason my Twin never sounded too hot at 50 watts.

Heres what I think I will do: The Twin has new speakers, so I am going to sell it. Then I think I will buy an Avatar cab with some 8 ohm Celestions and build a 50 watt Dumble. The reason for the 4 ohm cab is that I have a '64 Bassman head (with presence knob - really makes it!) that I could also power the cab with. It the Dumble knocks me out with tone, then I will sell the Bassman head too. Sound like a plan?
Whit

[BobW]

Tonegeek

tried this once on the aforementioned Twin (switch lifted cathodes from ground on 2 tubes) and in the 50w mode it took the life out of the sound. Is this where I need a multi-tap xfrmer so I can switch the speaker Z when I go to the 50w mode? Maybe thats why my sound was so dead.

Typical Fender OTs and any other well designed Tube amp can handle a 100% mismatch on the output impedance w/o any problems. Remember, the impedance is not constant but changing w/frequency, the same hold true for a speaker. Also any impedance ratio change to the primary (tube side) is reflected to the secondary (speaker) side. You will NEVER acquire perfect matching, but if you want to compensate for a change in the secondary, a simple toggle switch will perform the same as a multi- tap OT.

[Tonegeek]

Typical Fender OTs and any other well designed Tube amp can handle a 100% mismatch on the output impedance w/o any problems.

Agreed. Fenders seem to be very tolerant of mismatches, although I know of Marshall users who have smoked the OT by not having the impedance switch in the correct position.

The question I am having trouble addressing is why the sound is not as good when you pull 2 tubes from a 4 tube amp, or lift the cathodes on 2 of them as I did in my Twin. I assumed it was from the impedance mis-match, but maybe there is another explanation. Sorry this thread is getting off topic a bit...
Thanks,
Whit

[Bob-I]

The question I am having trouble addressing is why the sound is not as good when you pull 2 tubes from a 4 tube amp, or lift the cathodes on 2 of them as I did in my Twin.

I can't say that my experience was the same. I often ran my twin on 2 tubes when one of the 4 blew. I'd remove the other one in the pair and finish the gig. Not only didn't I notice the difference, no one in the band did either. But each amp is unique as are speakers. I was using a single 8ohm JBL at the time.

Sorry this thread is getting off topic a bit...
Thanks,
Whit

No, this is an important topic.

[Tonegeek]

Not only didn't I notice the difference, no one in the band did either.

It could be that something was wrong with my remaining tubes when I switched down to 2, or that the bias was not as matched with those 2 causing some crossover distortion. I won't have worry about any of this with the amp I am building since it will using only 2 tubes for output. I believe I will incorporate bias test points and maybe even individual bias adjustments for each tube.

[Bob-I]

......it will using only 2 tubes for output. I believe I will incorporate bias test points and maybe even individual bias adjustments for each tube.

I put all this into my 3 Dumble channel amp. I agree that these are great to have. I can't count the number of times I've opened up an amp to make a little tweak or how many times "matched" tubes didn't bias evenly.

[Luthierwnc]

Your donor amp is probably worth more than just the components in the open market. This isn't the POV of the true artiste but if you need new speakers, new board, faceplate, different pots...what you have is a box, chassis and iron. Some cowboy might get all lusty over your amp if it isn't too modded already. Plus he can carry it. FWIW.

The other guys have made an important point; when you're done, you're only half done. After the full power tests, you will probably make a lot of changes to dial in your sound. That doesn't even include fiddling with all the pots, tubes and cabs. These things will make a lot of different noises. No matter what you decide, you should end up with a rig that you'll love. Have fun and let us know how you do.

Skip