My take on Eric Johnson's Steel String Singer #005

[martin manning]

Still missing the 4n7 Martin! Which would be about as useful as bacon flavoured toothpaste.

Nothing wrong with that! My dog loves that stuff! But seriously, you keep saying you are comparing your filter arrangement to the one I proposed, yet you keep leaving parts of it out?!?

[Guy77]

Still missing the 4n7 Martin! Which would be about as useful as bacon flavoured toothpaste.

Guy, I'd have to make a new set of comparisons to really hear what the different values mean with respect to character of the amp. What were your observations?

What I have observed is that when voltages come down to 240v on the Phase Inverter and about 220v on the Cathode follower that amp develops a little more compression, sounds smooth and lush sounding (if thats a discription). But when its running at 300v and 340v respectively it becomes tighter and less compressed sounding which many people may like with this type of amp but I was going for something different.

G

[rootz]

There you go Martin.

First sim: your filter (now with 4n7 and 820k instead of 1 meg) vs my current setup
Second sim: your filter vs my previous setup

Observation one: your filter is adding more and more mids and shifts the mid dip like my previous filter did
Observation two: as you mentioned the steps are more even, which would make the low filter better in some ways.

Now my previous conclusions/preferences are still intact: I found the high filter to be too aggressive (big steps, too much mids added) and this was especially true from 680p upward.

The latter might still be a matter of preference from my side. I like my amps a bit on the dark side I guess. But I still wonder: who finds the high value high filter caps useful in an 005? Who actually uses a 002 based filter section in an 005? Did dreric?

[martin manning]

Thanks for that. Of course the TMB controls can be used to raise or lower the effective ranges of the step filter settings, and to change the overall EQ shape, so you can vary all of that to taste from the front panel. For example, the treble control can shift the the treble peak of the EQ curve by almost as much as the full range of the step filter setting.

The big spike in the output around 100Hz is an outcome of the output stage. The output stage is different from 002, 004: more Marshall like values, much lower global nfb. So the stage has got more gain and lower damping factor than most other Dumbles I know of. Maybe with the exception of the Bluesmaster? The load is modelled after one of my EVM12L speakers. Then simplified for use as a load ála the Suhr load box.

A significant part of the ~100 Hz spike might be the reactive load you are using. What are the DC resistances assumed for the inductors?

[rootz]

That 6m8 is around 0.5 Ohm. With these values the impedance is around 55 Ohm at the lower resonance peak. IIRC this is in line with the Suhr load box. I'd have to look the measurement of my 1x12 with EVM12L and combo with WGS ET65 (both 8 Ohm) up to see how close I kept it to real world.

[rootz]

Some comparisons:
1) 005 values PI vs ODS values PI, the latter having less feedback;
2) Same amp into simulated load vs into bare 7 Ohm resistor.

[Guy77]

I am building this amp with traditional style layout boards and thought I would post my build here so others that are interested can see it.
This will be 50 watts. I used a 820pf resistor to feed the reverb of the V1 plates instead of the 250pf seen else where just because I like my reverb a little darker sounding.
I mix the plate resistors with a bit of CF and MF just for my own personnel taste.
More pics later this week.
Transformers coming tomorrow!

Cheers
Guy

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[aumamps]

What are the voltages you are expecting? I am designing a similar build based off of what iron I have to work with (a 360 or 370RMS PT, 3.2k OT and a pair of 6550s) and I am just looking around to see what others are working with.

[jazzbass]

I am building this amp with traditional style layout boards and thought I would post my build here so others that are interested can see it.
This will be 50 watts. I used a 820pf resistor to feed the reverb of the V1 plates instead of the 250pf seen else where just because I like my reverb a little darker sounding.
I mix the plate resistors with a bit of CF and MF just for my own personnel taste.
More pics later this week.
Transformers coming tomorrow!

Cheers
Guy

20220822_191812.jpg

Hi Guy,

i'm thinking of building a # 005 too, i'm looking for a layout and boards to build it in a standard chassis. Can you suggest where I can find these things?
Thank you

Franco

[Guy77]

What are the voltages you are expecting? I am designing a similar build based off of what iron I have to work with (a 360 or 370RMS PT, 3.2k OT and a pair of 6550s) and I am just looking around to see what others are working with.

Hi , the amp is done and sent off to a happy customer but I took lots of pics and voltage reading and will post everything here in a day or two.
This is definitely an amp worth building. 6550s will work great here too. My preference lately has been the JJs but I am sure others will work fine too. I did a similar build a while back with the JJ 6550s and they had a nice tight driven sound when run with an overdrive pedal. The 6550s had that EL34 driven sound thing happening and the 6L6s had the beautiful cleans!
This is a nice FAST amp.

Cheers
Guy

[Guy77]

I am building this amp with traditional style layout boards and thought I would post my build here so others that are interested can see it.
This will be 50 watts. I used a 820pf resistor to feed the reverb of the V1 plates instead of the 250pf seen else where just because I like my reverb a little darker sounding.
I mix the plate resistors with a bit of CF and MF just for my own personnel taste.
More pics later this week.
Transformers coming tomorrow!

Cheers
Guy

20220822_191812.jpg

Hi Guy,

i'm thinking of building a # 005 too, i'm looking for a layout and boards to build it in a standard chassis. Can you suggest where I can find these things?
Thank you

Franco

Hi everyone, Ciao Franco. Just posting a final update on this build. I used the top schematic in the attachment below to complete the build. I left out the 33p cap that went across the 1 meg resistor. Instead of the 500p cap that feed the reverb I went with the stock 250p cap. I used Rootz's values for the High Filter caps so my last cap was 500p. This way the Highs increased more gradually. I found this beneficial in dialing the High Filter. I felt I didn't need anything beyond 500p though others may prefer higher values.

UsedTopSchematic.png

Regarding the layout my first pic shows how I drilled out the boards. Sorry I dont have any template since I drill these by hand, though I have a new CNC in the shop that I should use instead.
I found that I didnt need as my Reverb as the original circuit was providing so I reduced both reverb pots to 250KA send and 100KA return. This also helped control any feedback I was getting from the tank since this was built into a 15in Combo and it placed the reverb tank fairly close to the speaker. BTW these Eminence 1518 spk sound amazing!! I recommend to anyone building a D-Style amp. The cleans are rich and lush and full of body and when driven the sound stays together nice and doesn't fall apart. A nice warm and tight enough sound when driven! I am sure the 59oz magnet helps a lot.

Regrading the transformers I used they were Hammond 291CX and output was 1760L. I used a 2 x 194B chokes.
My voltages for all preamp tubes came very close to what is in the schematic attached. My power tubes ran at 445v with 120v wall voltage. I wanted my v1 a little hotter is I ran it at 210v. I went with Phase inverter values from a #124 and also used the same negative feedback values as a 124. I also added a boost switch to the circuit that bypass the ground for the MID and Bass pots. This gave the amp some cool driven sounds when cranked.

Cheers
Guy

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[Bombacaototal]

I was checking some picture of AN version of this amp and I found intersting the tube wiring for 6550. He is floating the grid stopper instead of using PIN 1, and I always thought 6550 does not use PIN 1, similar to 6L6. The spec sheet of 6550 (attached) says that PIN 1 is base sleeve. He has two black wires there, maybe one to ground and one to the other tube to accommodate for EL34? Is it fine to wire this tube socket as a 6L6 for 6550 (with correct screen resistor)

[sluckey]

I believe that metal base on the 6550 is actually connected to pin 1. You don't really want your pin 5 signal and bias voltage on that metal base, do you?

[martin manning]

It can be, but some brands may not make that connection. I’d just do a multimeter check to find out.

[Guy77]

I was checking some picture of AN version of this amp and I found intersting the tube wiring for 6550. He is floating the grid stopper instead of using PIN 1, and I always thought 6550 does not use PIN 1, similar to 6L6. The spec sheet of 6550 (attached) says that PIN 1 is base sleeve. He has two black wires there, maybe one to ground and one to the other tube to accommodate for EL34? Is it fine to wire this tube socket as a 6L6 for 6550 (with correct screen resistor)

Hi, I ran 6550 tubes in my Steel String Singer #005 build that I documented earlier in this post for a while. I switched back to 6L6 tubes before shipping it to a customer.

I used PIN 1 to anchor my grid stopper and it was no problem. I used JJ 6550 tubes and with those tubes PIN 1 is not connected anywhere. Other tubes such as the Tung Sol 6550 maybe be different and this maybe why the SSS #005 you posted had the grid Stopper floated. I believe that amp used the Tung Sol 6550s

Cheers
Guy