Hybrid build in progress

Luthierwnc · Post by **Luthierwnc** » Sat Sep 02, 2006 4:33 am

Oh yeah, I got the cab today too. Some assembly required.

Normster · Post by **Normster** » Sat Sep 02, 2006 6:07 am

Dang!!! Now THAT'S a workshop!

Luthierwnc · Post by **Luthierwnc** » Sat Sep 02, 2006 10:04 am

It's a dirty one. Luthiers are supposed to have Geppetto-like shops and perform zen ceremonies to sharpen their chisels every morning. I just finished a cabinet job for my wife's business and waited to sweep up until this cab was roughed out. Then, of course, I didn't get to it for a month. Somehow, I've come to terms with the guilt.

Luthierwnc · Post by **Luthierwnc** » Tue Sep 05, 2006 12:37 am

Primary soldering is done. The next step is to check it against the schematic. The FET is an afterthought so I needed to install it near V1 for lack of real estate. sh

Normster · Post by **Normster** » Tue Sep 05, 2006 2:54 am

That looks great! BTW, early Dumbles mounted the FET in the back so you're probably OK. How are you going to mount the chassis in the cab?

Luthierwnc · Post by **Luthierwnc** » Tue Sep 05, 2006 11:46 am

If it follows form, I'll use four 1/4" bolts through the bottom and bronze furniture capture nuts (the kind for knock-down desks) on top. Works well and is fairly elegant. sh

Luthierwnc · Post by **Luthierwnc** » Sun Sep 17, 2006 5:55 am

Primary soldering is finished. I ended up pulling the FET. It worked but not my sort of sound at all. The Dumbleator ended up at 375 VDC on the send plate and 311 on the return. From the screens there is a 10k resistor to the first cap and a 47k resistor to the return plate. Also after the 10k resistor is a 2k2 resistor to the next cap and the send plate. I used two 32uf caps.

Other volts are:

B+ 419 (7591 tubes biased at 31 ma)
Screen 416 (fixed bias)
plates 278,277
OD1 216 OD2 223
CL1 211 CL2 207 (has a 150k to ground on B+5)

One problem I need to tweak: when I switch the Dumbleator on, there is a quick whine that rises in pitch until it is inaudible lasting about 1/2 second. I put a 56 puff suppression cap to ground before the PI input cap. It completely killed the noise but took some high end off. The wire from the switch to the PI cap is not shielded so I'll try that tomorrow. Either way I am adding some capacitance to the line. I'll try a 10 puff cap too. If anyone has another idea, operators are standing by.

Next up is making the cab and picking a speaker. I have been testing it with a Tonespotter. The amp is about as loud as I expected and very "sweet" sounding. It breaks up sooner than the HRM. That narrows the field on speakers since the winner will need to be pretty clean with more than average bottom. I'll try it with a RWB tomorrow.

What should we make next?

Skip

dogears · Post by **dogears** » Sun Sep 17, 2006 11:38 am

Skip,

Your voltages are whacked..... This is what you do. You have two parallel strings running from the screens. 47k to 56k to the return plate of the Dumbleator. Then another 75k to the send. The caps go after the dropping resistors! You did something wierd if I understood what you wrote. screen>47k>cap>75k>cap is what you want with the return amp plate fed from the first cap. Send from the end.

In parallel from the beginning, use the Hybrid A dropping string for the phase inverter and V1 and V2.

You will have 20v lower on V1 and V2 and the Dumbleator will have about 220v on the plate (measure at the tube) and 230v or so on the send.

Leave the 150k load resistor at the end.

The Dumbleator is one series string and the amp gets another. 2 strings. I think you did something different.

There is no other way than this. Do it right away. BTW, never ever use caps to ground.

Luthierwnc · Post by **Luthierwnc** » Mon Sep 18, 2006 1:42 am

Scott, I'm afraid you lost me. The only way I could figure out how to have the return come off the first cap but have the send with a higher voltage was to add an extra resistor. This is what I had originally but geared for the voltages Gary used on his reverb-o-loop. I changed the values to get it more into the range you gave.

Thanks, Skip

Normster · Post by **Normster** » Mon Sep 18, 2006 2:09 am

Skip, I thought it was a bit strange at first, but here's how I did it.
1. Screens to 47k resistor
2. Return taken from B3a
3. Send taken from B3b after 75k resistor.

Of course, I could be way out of whack as well.

dogears · Post by **dogears** » Mon Sep 18, 2006 2:21 am

This looks good Skip. Dumbleator plate is 100k though. Use 2.2k/24k/2.2k for the amp string too.

Luthierwnc wrote:Scott, I'm afraid you lost me. The only way I could figure out how to have the return come off the first cap but have the send with a higher voltage was to add an extra resistor. This is what I had originally but geared for the voltages Gary used on his reverb-o-loop. I changed the values to get it more into the range you gave.

Thanks, Skip

Luthierwnc · Post by **Luthierwnc** » Mon Sep 18, 2006 2:34 am

Thanks guys;

I'll see if I can get on that tomorrow. BTW, Scott, how do you like those Scumbacks?

sh

Luthierwnc · Post by **Luthierwnc** » Mon Sep 25, 2006 3:12 am

The chassis is now done and I have to get serious about the speaker. I have tried it with a Tonespotter, ceramic Silver Bell, alnico Blue Dog and a RWB. All of them sounded pretty good in their own way. So far my favorite is the RWB although those 7591's need a little more help in the bottom end. The amp is also dirtier than the HRM. Right now, the leading contender is the Swamp Thang. This amp definately will sound better with a low, clean American voice.

Comments, questions, suggestions, free speakers?

Thanks, Skip

skyboltone · Post by **skyboltone** » Fri Oct 06, 2006 4:54 am

You got clips?

Dan

Luthierwnc · Post by **Luthierwnc** » Fri Oct 06, 2006 2:14 pm

Naw. I don't have any recording gear. When I'm not playing alone I'm playing where beer is served.

Here is the status of the new build. I am rewiring it as an HRM. My original intention was to make something I could play with a Strat. In this case, a USA Custom with 62,57,57 Kinmans. I completed it as a Hybrid but the smaller tubes and lower plate volts made it break up 1 or 2 too soon, especially with the built-in Dumbleator. This weekend I should finish the rewire and start working it through the in-house speakers selections. My sense is that the D-lator is absolutely mandatory for making a Strat work. The original hi-power HRM build supports that theory.

I should also get the cab dovetailed this weekend. The boards are joined so I just to plane them and make the x-cuts. The plan is to mount an Alesis Picoverb in the cab for reverb or delay.

Coming full circle, I decided to build a Dumble clone as a result of a little Ampmoot some friends and I had here in Asheville last fall. We borrowed a friend's cabinet shop and each brought up to three amps; a combination of homebrews, vintage and sentimental favorites. For about three hours we made noise and I got to play and listen. My clones and originals sounded really good for lead tones but lacked clarity on the clean and rhythm tones in a big room.

I enlisted Harris (an ampgarage member) and we both started researching the build to each make one. At the same time, this forum came on line which was a huge help. Thanks to all, BTW.

It is probably time for another Ampmoot. A different location is in order and one of the guys has beaucoup recording gear. If I can get something off the ground, we'll record some D clips with various instruments, speakers and players for posterity. In the meantime, I'll finish off this thread as soon as the thing is (mostly) done.

sh

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Hybrid build in progress

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almost done

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Mine's done too

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Time to buy more stuff

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Re: Hybrid build in progress