New 70's style build up and running. (Thanks!!)

[David Root]

Sorry, double post.

[makrisp]

Your amp is beautiful!

Enjoy it!

[jelle]

David,

you are very welcome! Have fun with the amps.

Jelle Welagen

[crbowman]

+1 on kudos to all those crb acknowledged.

I'd also like to thank Jelle Welagen for all his help, including having two of his great cabs made for me, and answering a grundle of q's I had about a #40 build in a Princeton Reverb chassis and cabinet, which is next after I finish my #124 now in progress.

crb, I have a pair of those Tungsol 6L6s reserved for my #40, how do you like them so far?

Do you use yours on the 4 ohm output into an 8 ohm speaker, as the legend has it about #40??

I've definitely picked up some chops from Jelle as well. He certainly deserves props!
So far I've liked all of the new Tung-Sol stuff. I've got a set of the 5881's in my old Bassman and love 'em. I think the short bottle 6L6's sound very comparable. I've yet to try this beast out in a band situation so my experience with these tubes is kinda limited, but so far I really like 'em.
They seem to sound best biased kinda cold, which seems to suit the D circuit really well.
I'm using the 4 Ohm tap as per HAD, with an 8 Ohm 1X12. Took some real convincing to make me comfortable with the mismatch, but it sounds great with no excessive heat so far.

[marcos]

Looks very nice, actually a little better than the real thing!
I noticed a ceramic treble cap, the 70s amps I have seen all had a silver mica, FWIW.
Good idea the keep the eyelets for the OD trim pot, I imagine you might
find this very useful some time.
I used my amp (one of #40´s brothers) for decades with a 8 ohm speaker on the 4 ohm tap, so I wouldn´t expect any problems here.
However, in the last years I have preferred the amp´s tone when running into a 4 ohm load.
One thing I have never tried myself is replacing the cathode resistors with something else, I never thought this would make much of a difference, but we´ve been surprised so many times, haven´t we?
In the case of the plate resistors I totally agree with jelle (as always):
The RN 65 are very smooth and clean, nowhere as harsh as other metal film resistors, so I would stick to the formula.
Then again, Andy Fuchs uses something else , and with convincing results
Keep rockin´guys
Marcos

[crbowman]

Looks very nice, actually a little better than the real thing!
I noticed a ceramic treble cap, the 70s amps I have seen all had a silver mica, FWIW.
Good idea the keep the eyelets for the OD trim pot, I imagine you might
find this very useful some time.
I used my amp (one of #40´s brothers) for decades with a 8 ohm speaker on the 4 ohm tap, so I wouldn´t expect any problems here.
However, in the last years I have preferred the amp´s tone when running into a 4 ohm load.
One thing I have never tried myself is replacing the cathode resistors with something else, I never thought this would make much of a difference, but we´ve been surprised so many times, haven´t we?
In the case of the plate resistors I totally agree with jelle (as always):
The RN 65 are very smooth and clean, nowhere as harsh as other metal film resistors, so I would stick to the formula.
Then again, Andy Fuchs uses something else , and with convincing results
Keep rockin´guys
Marcos

Thanks Marcos.
Your contributions and expertise were essential in getting this one right, and are greatly appreciated! And you are absolutely correct about the mica treble cap. I just went back and looked at the photos of #40 on the Rob Livesey sight. We talk so much about the ceramics here that I made an incorrect assupmtion. I have an old Marshall cab that's wired for 4 ohms and it really rocks with this amp. But my main cab is a 1X12 Avatar with an Emi RWB. Easier on my back you know.
Again, thanks for your input!
Carey

[fp2000]

Marcos, you mentioned earlier about how great the FET circuit works on this amp. What is so special about it?
Is it the same FET circuit found on the other amps?
Please let me know your findings. I was about to try different fets but did not know where to start.
Thanks, great looking amp. Clips would be nice!

Frank

[David Root]

I just checked the pix of #40 on Rob Livesey's site. Lots of ceramics but I didn't see any silver micas, either dominos or brown drops.

[Matt J]

Awesome looking build! I hope it sounds as incredible as it looks! Did you do the label work on the chassis yourself?

[marcos]

Hi David,
assuming we are looking at the same pictures, you can see a small brown silver mica cap connected to the slope resistor, next to the 100n
orange drop bass cap.I did not download the pics from Rob Liveseys site,
got them somewhere else about 6 years ago.
I have not seen #40 myself, but three amps from the Santa Cruz days,
and all of them had silver mica treble caps.
I just wanted to point out that it is not necessarily correct to assume that
the ceramic treble cap is an important ingredient in the Dumble sound,
since HAD used both types.
Marcos

[crbowman]

Awesome looking build! I hope it sounds as incredible as it looks! Did you do the label work on the chassis yourself?

Thanks Matt.
The chassis came already screen printed. Got it from a member here named Nachanis. Some of the holes aren't drilled in the right places, so I had to re-drill 'em, but the screen printing is pretty much spot on. Never had much luck with that myself.

[67plexi]

crbowman,Looks Great love the black boards, Did you have a bias tap
on the JTM 45 power transformer ? or did you take it off the HV secondary
lead with a 220k I can't tell from the photo.

Way to go, Steve.

[David Root]

Thank you for the additional info Marcos. I missed that one, it kinda merges into the board. Are these the same micas we can buy now? It looks similar.

[marcos]

Hi David,
the silver mica treble cap is out of the amp now (replaced it with a 330 pF silver mica), is labelled 510 pF, and looks unlike any of the caps available
these days.I have several caps from different manufacturers, my favourites are made by CDE I believe, and they all look different.Maybe when I get around to it I will post a picture of the cap, some of the guys here might know what it is.

[crbowman]

crbowman,Looks Great love the black boards, Did you have a bias tap
on the JTM 45 power transformer ? or did you take it off the HV secondary
lead with a 220k I can't tell from the photo.

Way to go, Steve.

I had to take it off the HV secondary. I wound up using a 120K resistor. I started at 150K and just didn't get enough bias voltage. The black boards are 1/16 G10 and I doubled all of them up as per HAD. I thought long and hard about using fish paper boards, it kinda looks like that's whats in #40, but decided against it.
Thanks Steve!