5E8A build

[husky]

The other key that was a tough nut to crack on the repro amps I made was the tone of the cabinet. Baffle being VERY important.

Care to share any more regarding the baffle?

Floating? Pine vs ply? Thickness?

Any added stiffener?

Thanks!

It was old, thin, super flexible and falling apart.
They pretty much float on those amps and it is a big key.
The baffles had a tone that was very important. Old Pine for the cab and the crappiest Ply we could find for the baffle to capture the same tone as his original. That was much harder than duplicating the amp for me.

[husky]

I use all NOS 6072's in the first few tube sockets as I find that swapping in 12AX7's make this amp unbearably gainy. Any comment on the tube choice that Clapton uses? (tube type, brands, etc..).

We used stock Sovtek Fender 5881, reliability was paramount, we tried some highly regarded and recommended Chinese 6L6's at the time but they didn't last long and actually blew at a gig. The only preamp tubes that sounded "correct" were NOS 12AY7's the 6072s I tried at the time were too microphonic. I did mount the preamp tubes with rubber grommets like his original. Oh the OT was very special and hard to track down. I found someone who knew all about it though and made them custom for those amps, his name was Dennis Hoyer, I think he is still around and they were not cheap but had a special tone to them and were way overbuilt.

[Cliff Schecht]

That's funny, I've had quite the opposite experience between 12AY7's and 6072's. Before this summer all I had were a few 12AY7 pulls of unknown strength and did my basic testing with them. I brought the build to a bud in Lubbock who deals in lots of vintage amps and had owned a few real tweed Twins. At first he noticed the amp didn't sound quite right, it wouldn't clean up well and was too noisy. He walks to the back and whips out some untouched 6072's (I think JAN-Sylvania) and these brought the amp to LIFE.

I picked up a big mix of new and slightly used 12AY7's and 6072's cheap this summer at a ham radio swap meet this summer but haven't even plugged any of these tubes into the Twin. I'm expecting the 6072's (ruggedized 12AY7's) to sound better than the AY7's but I have the highest hopes for the few 6072A's that I've found. The few I'm really excited about trying are the GE 5-star 6072A's, every GE 5-star tube I've used (5751's mostly) sound fantastic and are very well built. I think the RCA 6072A's are also supposed to be titties but I don't have any to try out as of now..

As for the output transformer, I'd love to hear more details if you have them but I feel like I'm prying for information now. For me at least it's more just a curiosity because I'm probably leaving the Stancor hifi iron I have in there, it sounds super with this amp already.

[husky]

As for the output transformer, I'd love to hear more details if you have them but I feel like I'm prying for information now. For me at least it's more just a curiosity because I'm probably leaving the Stancor hifi iron I have in there, it sounds super with this amp already.

Well it was stock very overbuilt (so adding the two extra tubes wasnt a problem) and was a Triad of which they actually supplied Fender with two different primary impedances. Dennis happened to have all the original prints so he was able to remake them at a cost of something like $300 each, no matter it was Fenders dime. This was a while ago and I do have the specs written down somewhere but probably in a moving box.

[David Root]

The original 5E8A tubes were mounted on rubber grommets? First time I heard that. But I've never seen inside a real one.

[Cliff Schecht]

There is a guy over at TDPRI that has a waay cool collection of vintage Fender amps. He's posted pictures of his twin Tweeds (yeah..more than one) and I don't recall ever seeing anything goofy like that.

[Herec]

There is no reason other than that the adapters I made are built from old relays and are I think about 2" tall. Tack this onto the length of an ST-shaped 807 bottle and I'm at I think about 10" tall worth of tube. If I want to mount this amp into it's own head cab with the controls facing up and tubes facing down (i.e. traditional tweed Fender style) then I need at least 10" of clearance on top of the length of the chassis. In my case it makes the amp unbearably tall for a head but if I put this amp in a combo then I could use 807's no problem. I'd probably use some sort of homemade tube retainers if I build a combo though.

Ah ok. They looked big when I looked them up, didn't realize how tall they actually were!

Where do you put the low-z choke in the circuit? Does it use the inherent capacitance of the 807 for some LC type of low-pass filter?

[ampdan]

The original 5E8A tubes were mounted on rubber grommets? First time I heard that. But I've never seen inside a real one.

Every tweed Fender I have ever owned/seen had the sockets isolated with rubber grommets.

[Cliff Schecht]

There is no reason other than that the adapters I made are built from old relays and are I think about 2" tall. Tack this onto the length of an ST-shaped 807 bottle and I'm at I think about 10" tall worth of tube. If I want to mount this amp into it's own head cab with the controls facing up and tubes facing down (i.e. traditional tweed Fender style) then I need at least 10" of clearance on top of the length of the chassis. In my case it makes the amp unbearably tall for a head but if I put this amp in a combo then I could use 807's no problem. I'd probably use some sort of homemade tube retainers if I build a combo though.

Ah ok. They looked big when I looked them up, didn't realize how tall they actually were!

Where do you put the low-z choke in the circuit? Does it use the inherent capacitance of the 807 for some LC type of low-pass filter?

Are you talking about the plate cap RF choke? This is built with a 10 Ohm, 2W CC resistor in parallel with 10 turns of wire. I guess you could look at it as part of an LC low-pass network but really the idea is to prevent the stray inductance from the long plate cap lead interacting with the plate capacitance of the 807. The choke looks like a 10 Ohm resistor at low frequencies and starts looking more and more inductive (i.e. higher impedance) as frequency increases which helps keep RF oscillations squashed.

[Herec]

The plate connection is on top of the glass of the 807, correct?I looked at the data sheet and at first glance it looked like it just disappeared into thin air, but on second glance it said "cap". Wild stuff.

Not to derail the thread, but you mentioned you just got your bachelor's in EE? I'm about to start my 4th year of 5 for mine.

[Cliff Schecht]

Yeah just finished my bachelors last year, I took 5 years as well. I jumped right into PhD after my bachelors so I'm still looking at a minimum of two years, probably closer to three. As long as I'm getting paid I don't mind the workload and doing research sure beats waking up to a 9-5 job 5 days a week (as I'm doing this summer). Are you doing any grad school? What are you specializing in?

[Herec]

I have no future plans as of right now haha. I'm at Northeastern University which has a co-op/internship program where you work for 6 months then take classes for 6 months. Its nice to have a change of pace, and I feel I learn more when working/doing my own thing than in class.

We don't have any defined specialties at the NU but for tech electives I'll be taking as much analog design and DSP stuff as I can. I have a minor in Music Industry too.

[Zippy]

Yeah just finished my bachelors last year, I took 5 years as well. I jumped right into PhD after my bachelors so I'm still looking at a minimum of two years, probably closer to three. As long as I'm getting paid I don't mind the workload and doing research sure beats waking up to a 9-5 job 5 days a week (as I'm doing this summer).

Been there... Oh yeah. My B.S./M.S./Ph.D. ended up taking nearly 12 years but, like you, I was digging it so much that it didn't really matter. Imagine my surprise when they told me I had to leave and make a career somewhere else! And now I'm teaching grad classes there part time...

Enjoy the ride!

P.S. Don't wait 'til you're done with the Ph.D. to find a job.

Recommended reading: "A Ph.D. is not enough".

[David Root]

Cliff, here's what HiTest Guitars sells NOS 5751s for:

RCA 5751's, black plates…$50.00

RCA 5751's, Command Series…$65.00

RCA 5751WA's, 1950's black plates with triple micas…$65.00

Raytheon 5751's, triple micas…$65.00

GE 5751's, 1950's military stock, black plates with triple micas…$60.00

GE 5751's, 1950's military stock, grey plates with triple micas…$50.00

GE 5751's, early 1960's military stock, grey plates with triple micas…$40.00

GE 5751's, early 1960's military stock with double micas, strong value…$30.00

GE 5751's, 1960's 5 Star commercial series, grey plates, strong value…$30.00

Looks like the 5 star GE above is a sleeper!

And here's his GE 6072As (these are the only 6072s he sells):

GE 6072A's, 1980's JAN mil spec, black plates…$40.00

GE 6072A's, mid-late 1960's JAN mil spec, black plates. extra support rods…$50.00

GE 6072's, black plates, triple micas, 1950's-early 1960's military and 5-Star commercial stock…$70.00

So I think you are on the money with the 6072A, the top price is the black plate 5-Star or military at $70.00

[Cliff Schecht]

Jesus! I pick up most of those tubes for about 1/10th of the retail (on average) from a few great sources I have. The best part is my favorite dealer doesn't have a website, just email or phone and a stab in the dark as to what he has (usually just about everything). Not sure if I'd post his email/number publicly but I wouldn't mind sharing his contact info with the regulars..