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Building an EFB Dynaco ST-35 restomod in 2026

rupes2

rupes2

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I keep getting sucked back into this hobby :)

I decided I wanted to experience a tube amp. I was drawn to the ST-70 at first and dismissed the ST-35 due to its lower power. Then I read about the legendary Z565 output transformers and EL84 tubes. What clinched it was learning about all the work Dave Gillespie put into improving these amps and his EFB modification. I love a restomod.

I found an SCA-35 that had been on FB for a while and decided to build a new ST-35 using its transformers.

For anyone interested below are the prices (without taxes / tariffs / shipping) in 2026.
This does not include transformers, tubes, and EFB board mounting hardware. Also, I did not get a cover.

DescriptionVendorCost
Chassis, hardware, power cord, fuse holder, rca jacks, binding posts, 5 lug strip, tube sockets, hook up wire.dynakitparts.com$243
Dave Gillespie boards (PC-13 + ST-35 EFB).tronola.com$60
Components for above boards.Mouser + Digikey$92

The attached image is everything except the power cord, hookup wire, and mounting hardware.
 

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Welcome back!

Good choice. You will not regret it. Easy to build and a joy to listen to. So, for about $700-$800 and your time invested you will have a brand new ST35 sounding at its very best. I know because I did the same recently, using a SCA35 donor, except I also needed a new replica power transformer.

Keep us informed of your progress.
 
I don't have DG's boards, but my Dynakit ST-35 is my favorite amp. I installed the bias kit and 62 ohm choke from dynakit to mine.
I originally had JJ 12DW7's in mine, but thwn bought a pair of NOS GE's that I really like.
Enjoy the build, you won't be disappointed!
 

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I was lucky to find my 35 here locally along with a PAS3, and I think I'm only the second owner of the set.
The original owner had a set of Telefunken's in the 35, but those were sadly beyond my budget. I picked up a set of NOS USSR "Reflector" tubes which sound really good.

This setup sounds amazing. Keep us posted on how your build goes!

IMG_8099.jpg IMG_5250 2.jpg
 
Markoz said:
I was lucky to find my 35 here locally along with a PAS3, and I think I'm only the second owner of the set.
The original owner had a set of Telefunken's in the 35, but those were sadly beyond my budget. I picked up a set of NOS USSR "Reflector" tubes which sound really good.

This setup sounds amazing. Keep us posted on how your build goes!

View attachment 3856812 View attachment 3856813
Click to expand...
You don't need Telefunkens in your ST35. You do need a quartet of matched tubes, that is more important then brand. Matching implies new tubes, that's the only way to keep them matched.
 
Markoz said:
I was lucky to find my 35 here locally along with a PAS3, and I think I'm only the second owner of the set.
The original owner had a set of Telefunken's in the 35, but those were sadly beyond my budget. I picked up a set of NOS USSR "Reflector" tubes which sound really good.

This setup sounds amazing. Keep us posted on how your build goes!

View attachment 3856812 View attachment 3856813
Click to expand...
I have a set of 6P14P-EV's in my ST-35. Those Russian tubes sound really nice.
I have them in two other EL84 amps as well.
 
The new Dynakit stainless chassis is slightly modified to allow for a choke. This means that 1 of the 5 holes needed for mounting the EFB board is missing. Hopefully drilling it will not be difficult.
 
Lavane said:
Every time I see a picture of your amp I want to pull my amp out of my sysyem and add a pilot light. How hard was it to drill through that stainless steel chassis? Did you use a certain thoe a drill bit? Ive had bits weld there selves to stainless.
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Not hard. Used a chassis punch for a dimple to start drilling and just a sharp bit to drill the hole. Used (as always) a hand drill. Just have to be careful that it doesn't walk around on you (the reason for the dimple to start). You might consider a smaller starter hole, then drill it out with the larger bit. I also put a switch in the back. I really like the lamp because it's hard to tell whether the amp is on or off with the cover in place.
 
@Dave451 I see that you used the grounding points that Dave provides on the EFB board. @spantou01 did you do the same?

I was thinking of using the alternative method Dave describes (see attached) of using a ground lug. I don't like the idea of a ground lug on a slot so I would either use the nut that holds the frame stiffener on or an output transformer mounting nut.
 

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I used the grounding points on the EFB board. I soldered the wires to the EFB board before I mounted the board, and then soldered the other wire-end connections to their destination points.
 
rupes2 said:
@Dave451 I see that you used the grounding points that Dave provides on the EFB board. @spantou01 did you do the same?

I was thinking of using the alternative method Dave describes (see attached) of using a ground lug. I don't like the idea of a ground lug on a slot so I would either use the nut that holds the frame stiffener on or an output transformer mounting nut.
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I did indeed and didn't find it too difficult to work with. The amp is dead quiet with respect to any hum/buzz. Note that Dave gives a specific reason in the instructions for attaching the ground lug to the specified location.

Here's underneath with the switch and pilot lamp treatment, FYI, @Lavane. I also added the CL-80 you see.

IMG_4229.jpg
 
Lavane said:
Every time I see a picture of your amp I want to pull my amp out of my sysyem and add a pilot light. How hard was it to drill through that stainless steel chassis? Did you use a certain thoe a drill bit? Ive had bits weld there selves to stainless.
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Tube heaters work as pilot lights for me.
 
@Dave451 thanks for sharing that photo. It will be helpful when I start wiring things up. I bought a CL-90 and yours is the 3rd thermistor placement option I have seen.
 
egellings said:
Tube heaters work as pilot lights for me.
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Thats true with all my other amps, but I have a cage on my ST-35.
Unless your up close and looking through the cage you really can't see the tubes when they're lit up. My amps are plugged into Bluetooth controled outlets since the power switches are either on the back of the amps, or in the case of the ST-35 on the power cord. It's easier to use a remote control than to have to reach over hot tubes to turn them off. I've forgot to turn the ST-35 off a couple times and the amp was left on for several days at a time.
This hasn't happened with the other amps in my main system due to the tubes being exposed and easy to see.
 
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