We're On a Roll... Yet Another Express

[gktamps]

Howdy folks,

In between building a few Rocket variants with their own character and features, I thought it was time to build up an Express tribute. This is using a mix of parts bought from sellers here on TAG and elsewhere over the past year. Should be able to finish up the wiring today and get them all placed properly, but my cabinet and front panel are not ready yet so the pilot light and front panel placement will have to wait.

This is a nothing-special build - not a clone, no faithful attention to parts selection, unlike a few of the recent, gorgeous builds posted here lately(!) On the other hand, no bizarre deviations, just some smallish changes to come up with something a little different, and as a platform to play with different coupling and tone caps in various positions, as you can see in the photos.

PT is Pacific 25475.
OT is Heyboer 11415-2. I chose this over a 11415-1 on my shelf.
Chassis is RJ premium.
Caps are a blend of STK, SBE, and Solen, with F&T filter caps.
Back panel bias test points, 25k PEC bias pot (will be changed out for a 10-turn pot later).
PEC pots.
Bright caps connected to rotated volume pot, as I've done in all my builds (thanks to RJ).
UF5408 rectifiers, and 1N4007 flyback diodes hidden in the yellow shrinkwrap at the power tube sockets.

I know we have some really talented cabinet builders on TAG. I'm not one of them, so I try to spread my business around. This will be the third cabinet that Jeff Jones has made for me, and if you don't already know, he does really beautiful work. Not sure whether he prefers to build entire amps or is OK with supplying just cabinets, or what his usual turnaround time would be, but you might give him a try.

Once this is up and running and debugged, I'll try out Martin Manning's Presonance control - the Martinizer.

Comments and suggestions are always welcome from you all!

Cheers,

Greg

[jelle]

I like your cathode bypass caps. How do they sound ?

[Colossal]

Looks good Greg. I built a few hybrid platforms. How do you like those STK caps? Do you have any opinions about using flyback diodes vs. not?

[gktamps]

Thank you, Dave. With your hybrid builds, did you end up finding any preferences for your caps?

I bought 30 of these STK caps but this is my first time using them. They seem to get good reviews, and the Solens have been widely discussed for their properties. I used the Solens to couple the PI to the output tubes, but not elsewhere - just playing around. I used some NOS PIOs in another recent Rocket build but left them out in this one.

I have no opinion yet about the flyback diodes, but thought I'd install them and clip them in and out to see. Because Ken wrote he didn't like UFs in this position, I stayed with 1Ns Do you have an opinion on them? Looks like a lot of recent builds including your own (rather disgustingly gorgeous) build omit them...

Cheers,

Greg

[gktamps]

I like your cathode bypass caps. How do they sound ?

Yes, those are a little unusual. I've used them in a few builds and they seem to sound just great! Nice tight tolerance, and a lower voltage rating in keeping with what is demanded of them. Merlin, I believe, comments about avoiding the use of higher-voltage electrolytics than is required, to avoid more rapid degradation.

Pretty sure these came from Mouser...

[jelle]

Are you sure the caps are not installed backwards? I would expect the black band to be the negative side of the cap? Thanks!!

[gktamps]

Aaahhhh!
Nice save, Jelle. I made this mistake on my last build but corrected it before firing it up. Looks like I carried the same brain fade over on this one.

Confirmed the marking on the Vishay spec sheet. Don't see the same part in the Mouser catalog now, even with the same part number.

[jelle]

No problem!

[RJ Guitars]

You are off to a good start... thanks for the photos!

I really like the ability to set the bias without having to get inside the amp.

[gktamps]

Thanks, RJ. I like it too. Did it on my 6V6 KF60, another Express, and my JTM50, as well as my old Acoustic 165.

[Colossal]

Thank you, Dave. With your hybrid builds, did you end up finding any preferences for your caps?

I have no opinion yet about the flyback diodes, but thought I'd install them and clip them in and out to see. Because Ken wrote he didn't like UFs in this position, I stayed with 1Ns Do you have an opinion on them? Looks like a lot of recent builds including your own (rather disgustingly gorgeous) build omit them...

Cheers,

Greg

In the hybrids, I tried Solens, SBE 716P, Sozo, etc. The SBE sound pretty balanced with a lot of low end. The Sozos have a little more midrange content with the smear on the edge. The old Mallory PVC sound very musical to me with a lot of clarity. I really like them. Solens sound very good too.

As for the flyback diodes, I don't have an opinion about them save what I've read here; that they are audible after a point. I suppose I should put them in to see if I can hear them.

[M Fowler]

Greg the build looks good.

[gktamps]

Thanks, Dave, Thanks Mark.
GT

[dcribbs1412]

congrats
build looks great
are the bypass caps Tantalum?
interested to hear what you think of the STK caps.

Darin

[gktamps]

Thanks, Darin,

No, those are electrolytic, molded into plastic housings. They only do it for the smaller size caps.

http://www.mouser.com/ds/2/427/138aml-239889.pdf

I used to use smaller tantalum caps for pedals and inboard guitar circuits - how would they perform as amp bypass caps?

Cheers,

Greg