*New Build Thread* 2nd Gen Hybrid 50w footswitchable FET

[ToneMerc]

I know what you mean about finding the correct parts. I started rebuilding my HV, high plate skyliner last December and could have been done in December. However, I've been gathering the correct taper CTS pots for 6 months and I'm shy one 1M AUD 30% taper pot, so it's sitting waiting to be finished.

For D builds I'm still using Pihers that I gathered 4 years ago originally for Marshall builds. I've been fortunate to be to do some builds with 100% period correct resistive signal paths. However, if you can't do full signal paths there are strategic locations for vintage/NOS parts.

Personally, I've spent many hours studying Dumble pics to figure out the exact parts that were used and then try procure parts for these builds. This is really want makes these builds rewarding for me.

TM

[Dr d]

Im assuming the plate resistors are electras? Do you mind me asking what make the greenish looking bypass resistors are on the cathodes?

No, those plates are Mepco/Electra and the cathodes have the Electra. To be 100% Dumble correct the resistors should be all Electra. I have never seen that M/E in any Dumbles. When Electra took over Mepco they carried over the MFxC designation, then it was dropped that a few years later.
There's a physical and chemical difference between the two types, but I can't say if there's a tangible difference in audio beween them. Although #183 has a 22K Electra on V1a grid, HAD may have just used what he had on hand verses any type of preference.

Here's a couple of my builds with Electra and Piher resistors as well.

Cheers for the info, TM. Seems the builds are on to a new level now!

TM

[ToneMerc]

Cheers for the info, TM. Seems the builds are on to a new level now!

Dr d

I've found out that across the Dumble topology and variations it's the small things that matter and I'll ocassionally get an Aha, Dayum! moment, there's always new things to discover.

TM

[amplifiednation]

Well I'm very excited to hear how this NOS build compares to my new production 102. I used different wire too, no Teflon in this other than the relay and foot switch runs. Hopefully the amp sounds great! My 102 sounds really good with the Xicons and Dales, if the NOS makes a noticeable impact I'll be swapping out some parts very slowly to see what makes the biggest difference.

TM, thanks for the pics, your builds are epic

[ToneMerc]

Well I'm very excited to hear how this NOS build compares to my new production 102.

TM, thanks for the pics, your builds are epic

Taylor, my suggestion is go into this project with an open mind, it's a different circuit than the 102. I think the earlier circuits have more character than the 80's high plate circuits. I'll go through my stash, I might have to send you a nice NOS 12AT7 for the PI.

Thanks, you are doing a pretty good job there yourself.

TM

[RevD]

Great looking build! I plan to do one of these starting in Sept. I often wondered though, we spend so much time sourcing parts that HAD used and at the time I wonder if HAD was more concerned with the value of the part vs its composition? I mean he says I need part x, digs through his parts stash and puts whatever into the circuit if it meets the value he was looking for?

Anyway great job and thanks for that link of NOS parts that will come in handy when I get into this. I will say after doing some fender builds (Princeton and some tweeds and a plethora of Marshal builds) these Dumbles sure look intimidating, I guess you just have to take small bites and not get overwhelmed by the whole thing. Thanks for sharing your build with us!

Regards,

Don

[amplifiednation]

I found a couple guys selling Pihers in far away lands..mostly Marshall guys. Cool, but very expensive (220k at $5?!?). I wonder how the Beyschlag CFs compare. They are 1/4 the price.

I forgot the Bassman was tube rectified...so with a new Mojo PT I won't need an auxillary transformer...that was a nice find!! Thats the last part I need.

Thanks to Martin's help I got the FET biased up. Last night I drilled out new mounts for the extra relay and the FET board and installed them on the side of the amp.

I don't have any more of the nice backers for the relay boards that Jason sends with his chassis mount PCBs...any DIY ideas on approved non-conductive backers? I've been looking around the shop but haven't found anything that really struck me. I need to figure that out before I wire up the relay because once it's in, it's in for good!!!

Power up is scheduled for my b-day, next tues!!!

[ToneMerc]

I don't have any more of the nice backers for the relay boards that Jason sends with his chassis mount PCBs

Taylor, I hate to burst your bubble, those "nice" relay board backers that you used for your last build....I made those . I can send you some more and for the two mounted on the floor and wall, I can put #4 bushings in them as well.

TM

[talbany]

Taylor
shoot for 185 on V1a and low 190's on V2
These amps dig RCA 12AX7's
They can be a bit in your face so experiment around with some different value GNFB resistors and find one you and the 7581's likes..
It will be different than your 102 so give it some time for your ears and hands to discover the nuances and dynamics before you decide to start tweaking..Good Luck

BTW ...7581 should sound good also the Short bottle TAD's sound wonderful as well in this amp..NOS Blackplates even better..T


Tony

[Structo]

Most of you probably know about this but this is an excellent source of tube data sheets.

http://tubedata.milbert.com/index.html

[amplifiednation]

Taylor
shoot for 185 on V1a and low 190's on V2
These amps dig RCA 12AX7's
They can be a bit in your face so experiment around with some different value GNFB resistors and find one you and the 7581's likes..
It will be different than your 102 so give it some time for your ears and hands to discover the nuances and dynamics before you decide to start tweaking..Good Luck

BTW ...7581 should sound good also the Short bottle TAD's sound wonderful as well in this amp..NOS Blackplates even better..T


Tony

Tony between you and Mike I am getting extremely anxious to hear what these 2nd gens are all about!

I just got some NOS grids in both CF and CC and will get those replaced later today, PT should be here by the weekend. Choke, IEC, and more shielded cable get here today so I can mount up the PS board and start the heaters, I'll be happy when this is rockin and rollin!

[ToneMerc]

Taylor, those backers and other goodies I will mail today. Also, will send you 1.2, 1.5, 1.8 & 2.2K to try at the GNFB position.

TM

[talbany]

Taylor...I've found
The CF will yield a bit more clarity definition and bite on the top end
The CC will mask clarity giving a smoother tone with less bite
The difference will be subtle but noticeable none the less..

The CF for me work the best for live and studio work and the CC sound the best standing directly in front of it in my studio..
A matter of taste and application..

I would start with the CF roll some tubes and if it's still to much go to the CC
Again Good Luck!
Tony

[amplifiednation]

Thanks you guys rock!! I appreciate the help and the parts!!

[angelodp]

That amp is gonna rock, congrats Taylor.

Ange