3rd Gen started

[dorrisant]

Plate wires in general should not touch the cathode wire or grid wire. Move them around with chopsticks while operating to hear the difference.

That said, it does look gorgeous!

[ijedouglas]

Plate wires in general should not touch the cathode wire or grid wire. Move them around with chopsticks while operating to hear the difference.

I'm not sure that Mr Dumble subscribed to that philosophy It is pretty well documented that he liked to run the plate of Vxb alongside the cathode of Vxa. While I agree on the grid wire not touching, take a look at some of the gut shots around V1, there are a few examples of the plate wire elevated close to the exposed part of the grid coax. Try it .... You may be surprised

[ijedouglas]

It lives!!!

I thought I had a bad PT. When firing it up I got 340V on the plates and it sounded horrendous. After a lot of head scratching and calls to friends I pulled the power board only to realize I had missed a jumper between the incoming B+ and the reservoir caps.

First impressions: It has a smooth singing sustain in clean and breaks up earlier than I expected. The OD has a lot more gain than I expected. OD is also a lot smoother than I imagined these amps to be. Controls seem really nice and balanced. OD seems a little brighter than the clean. I am still waiting on some early 70's piher 56Ks for the grids so that may add some more bottom end and balance the highs better... still can't complain in it's current form though.

I still have the correct piher power string droppers on order but used some ABs for now. I didn't have a 27K so used a 22K that measured 25K.

PXL_20230304_021310616.jpg

PXL_20230304_021316397.jpg

[bepone]

First impressions: It has a smooth singing sustain in clean and breaks up earlier than I expected. The OD has a lot more gain than I expected. OD is also a lot smoother than I imagined these amps to be. Controls seem really nice and balanced. OD seems a little brighter than the clean.

Congratulations! After so many amps there are no surprises, results are in he ballpark from the first powering on!

pls feedback about bass quality? What output iron has been used?

[Colossal]

Beautiful build!

[ijedouglas]

Thanks all for the kind words.

pls feedback about bass quality? What output iron has been used?

The amp seems well balanced across the spectrum and I didn't notices too much/little bass. I used vintage 71 bassman iron

[jazzbass]

It lives!!!, I am still waiting on some early 70's piher 56Ks for the grids so that may add some more bottom end and balance the highs better... still can't complain in it's current form though.
I still have the correct piher power string droppers on order but used some ABs for now. I didn't have a 27K so used a 22K that measured 25K.

Hi Ian,

Demo, Demo, Demo...please

first of all congratulations, I noticed from the photos you posted that you have the 22K power string droppers resistor, did you replace the resistor? did you get the early 70's piher 56Ks for the grids?. Can you include in the discussion the voltages detected before the demo?

I want to build a 3rd Gen but with the variants that made me love the 2nd Gen Hybrid that I built and I love, like...to simplify the construction I will use the Tubetown kit to power the relays, master clean and master overdrive, effects in/out.....little things that will make it more current even if less equal to the Dumble project.

A hug. Franco

[bepone]

The amp seems well balanced across the spectrum and I didn't notices too much/little bass. I used vintage 71 bassman iron

great iron, good from the first start

[ijedouglas]

first of all congratulations, I noticed from the photos you posted that you have the 22K power string droppers resistor, did you replace the resistor? did you get the early 70's piher 56Ks for the grids?. Can you include in the discussion the voltages detected before the demo?

Thanks Franco. I havent changed any resistors yet... still waiting on parts

Voltages:
124VAC => wall

449.5 => plates
424.5 => B+1
283.5 => B+2
279.5 => B+3

V1
186.3 => A plate
1.35 => A cathode
191.2 => B plate
1.28 => B cathode

V2
189.5 => A p
1.38 => A c
193.9 => B p
1.31 => B c

PI
309.1 => plate
124 => cathode
262 => plate

[martin manning]

Looks great! Something is going on with the PI, though.

[ijedouglas]

Looks great! Something is going on with the PI, though.

Thanks Martin. Yeah, I'm going to try a couple different tubes today. It sounds good though...

Edit: bad PI tube. Put a nice balanced one in and measured again:

Voltages:
120VAC => wall

436.5 => plates
412 => B+1
290.3 => B+2
286.3 => B+3

V1
192.3 => A plate
1.365 => A cathode
197.7 => B plate
1.288 => B cathode

V2
195.2 => A p
1.396 => A c
200.4 => B p
1.317 => B c

PI
281.1 => plate
120.7 => cathode
275.7 => plate

I also changed the second dropper back to a 22K piher after talking to Charlie Wilson. Looks like most of the pics I have of 2nd/3rd gen amps are using a 22K and not a 27K as in the layout.

[Bombacaototal]

It lives!!!

I thought I had a bad PT. When firing it up I got 340V on the plates and it sounded horrendous. After a lot of head scratching and calls to friends I pulled the power board only to realize I had missed a jumper between the incoming B+ and the reservoir caps.

First impressions: It has a smooth singing sustain in clean and breaks up earlier than I expected. The OD has a lot more gain than I expected. OD is also a lot smoother than I imagined these amps to be. Controls seem really nice and balanced. OD seems a little brighter than the clean. I am still waiting on some early 70's piher 56Ks for the grids so that may add some more bottom end and balance the highs better... still can't complain in it's current form though.

I still have the correct piher power string droppers on order but used some ABs for now. I didn't have a 27K so used a 22K that measured 25K.

PXL_20230304_021310616.jpg

PXL_20230304_021316397.jpg

Looking fabulous! Well done!

[WhopperPlate]

The amp seems well balanced across the spectrum and I didn't notices too much/little bass. I used vintage 71 bassman iron

great iron, good from the first start

I need to hear this! Bravo , beautiful work!

[ijedouglas]

Update: I've swapped out a few resistors for period correct ones and this is really turning out to be one of my favorite amps. I ended up ordering a cab with vox grill and brown suede so I'll post an update when that arrives.

I also changed the PS dropper from a 22K to a 27K after reading a post with B+ voltages from an actual specimen. My V1 B+ was around 288V and the real ODS had around 260V. I found the amp softened a little and fattened up nicely... lots of fun to play.

Something I've been playing around with quite a bit is choke orientation. In chatting with Chris Merren a while back, he mentioned choke orientation. I built myself a small box with a switch to reverse the choke polarity. I had been just tack soldering the choke wires but I found this box way more immediate. After changing resistors in this amp (mostly early 70s 5% pihers) I found the amp became a bit more boomy. Swapped the choke and there was "the sound". The choke orientation makes a big difference (in this amp as well as all my other amps) . I would seriously recommend trying it on an amp you are familiar with.

PXL_20230326_194054193.jpg

PXL_20230326_194107163.jpg

PXL_20230316_204052068.jpg

[Colossal]

Let me say it again....beautiful build. And damn you for all those nice parts! Looks great.