More clean headroom for a homemade Tweed Super...

[Bruce / Mission Amps]

Well, I'm sure you already know most of this, but I'll run through my thought process... with the 5F4/5E5A/5E6/5E7/5E8 power supply, all of the current is being drawn through that choke, so there is a considerable voltage drop (my 14864 choke measures 125 ohms), especially at full power. When the OT CT is moved upstream of that choke, the plate voltage goes up, and since less current is being drawn through the choke, the voltage on the other side goes up as well. I have to assume that's why any of the Fenders after those I mentioned above have the plate supply ahead of the choke.

Having a CLC filter before any of the signal tubes makes good sense from a hi-fi perspective, but doesn't help when you're trying to squeeze every last watt from your guitar amp...

- Scott

OK sounds good.
I measured a small handful of my Heyboer 5F4/5E5a/5E7 chokes and got an average DCR of about +98 to 101 ohms.
They're rated at 200ma at about 5Hy and modern "copies" of real ones from the late 50's.
With respect to moving the OT tap, I have not done it but I'm not sure it will make much of a difference in head room vs benefits of the brute force PI filter concept.
Here is my thoughts.
The classic tweed 6L6 amps used a good 160ma to 180ma PT, so allowing for a 180ma across the 125 ohm choke would create a VDC drop of about +4vdc on your choke at near full power and or during a full charge recycle. On mine it would be about 3.3 VDC drop... or if you were cranking the amp to full boat, "rockin' dog" mode... maybe you could squeeze 250ma out of the B+ rail.... that would create a drop of about 8 vdc on yours and about +6.3 vdc across mine.
The second 16uF filter cap will give a nice smooth flow of charge power during the drop though so I'm thinking the 6 to 8 VDC drop across the choke, and subsequently to the OT's center tap, won't be very noticeable in dirtying up the clean headroom.
A nice thing about the brute force PI, CLC filter is that if the choke does get overly saturated with current and loose a lot of it's inductance, the two 16uF caps are looking like they are in parallel with a small DC resistance between, which still makes a decent filter and the B+ will not vary very much.

Some discussed this already, but I think the four items which will net the biggest differences in dirty vs clean headroom power with these amps, as I have experimented with is....

1.), use a bigger output tranny (the stock amp idles it frickin' power tubes at between 50ma and 60ma each through a 25 watt OT with X? ohms DCR). They really come to life with a good 40-50 watt OT.

2.) Use a stiffer rectifier instead of the old 5U4.

3.) Reduce the idle current of the power tubes so with the new plate voltage the tubes are running at about 16-18 watts max each

4.) Always use a 12AY7 in the first preamp tube socket.

As with everything I say.... it is only my opinion, but most of it is based on me blowing up my own stuff by experimenting... and yes, sometimes with customers gear too and then trying to fix it before the they get back.

[ThermionicScott]

Hmm, by my math, I get a 22V drop with 180mA across a 125-ohm resistance. Regardless, I leave my 5E7 clone with the stock CLC filter because I don't need much headroom in the shop, and it does a marvelous job of filtering hum (you can yank a tube and the hum still isn't objectionable).

Your four items make a lot of sense. The stock 5E7 (at least my clone with voltages within about 10V of the schematic) idles the power tubes even lower, like 11 or 12W each since it originally used 19W 6L6G's.

- Scott

[macpgh]

M I A

Lots of replies....but what ever happened to fats from wales?

It ain't over till the fats man sings

[allsavy]

simply put a 5751 in v1 and try a 12au7 in the phase inverter. I did this to my amp although it has a long tail pair PI I replaced the tail resistor with a choke to approximate a constant current source (not sure of the effect), I got a lot more headroom whereas before breakup was way too early. My amp was meant to be quite gainy and this tamed it.

Other mods that helped were: changing v1's plate resistor from 100k to 82k or doing a split-load (82k+18k) and changing the cathode resistor from 1.5k to 2.7k. I'm using humbuckers and get great headroom and blues tones.

[Bruce / Mission Amps]

Hmm, by my math, I get a 22V drop with 180mA across a 125-ohm resistance. Regardless, I leave my 5E7 clone with the stock CLC filter because I don't need much headroom in the shop, and it does a marvelous job of filtering hum (you can yank a tube and the hum still isn't objectionable).

Your four items make a lot of sense. The stock 5E7 (at least my clone with voltages within about 10V of the schematic) idles the power tubes even lower, like 11 or 12W each since it originally used 19W 6L6G's.

- Scott

22v at 180ma and 125 ohms is absolutely correct... I'm a dumb ass and wasn't thinking straight. My goof.
I'll sit it out for a while....

[Ammanford Fats]

The Fats man is back!!!

Hi guys,
Sorry I haven't been able to reply but my computer's been down for a few days.

Where to start???

Firstly, thanks to all for the replies and information - I have to admit that some of it went way over my head but I did manage to grasp the info about changing to low gain preamp tubes.

Secondly, the outcome of all this is that I actually managed to find a hand wired 5F6A chassis on the net for the same price as the guy was asking for the Super chassis - also, I didn't really want to buy an amp, immediately have it in the shop for some work and spend more money to try and change it into what I actually needed. I thought the Bassman chassis (with added 4 and 8ohm speaker outs and bias trimpot) would better suit my needs...BTW, I use a heavily customised Hollow Body Epiphone with 3 x P90’s, a Strat and our band play West Coast/Chicago Blues.

Just to answer a few of the queries…

The Tweed Super was a stock Weber 5F4 Kit with valve rectifier.

The amp was fine as I finished the gig off with my spare Strat with no problems.

My guitar checked out fine as well - a few days later I gigged it with my Blues Deluxe with no problems.

Well, my Bassman’s just been delivered and I can’t wait to hook it up to some speakers and start “Rockin The Boat”.

A Happy and Prosperous New Year to all,

Ammanford Fats.

[macpgh]

blues in england

Hey Fats,

did you ever play with a drummer named alan young? Or another guy that plays guitar & bass by the name of steve gould?

[Ammanford Fats]

Alvin Lee?

Do you mean the guys that played with Alvin Lee?

They're a bit before my time (didn't join my first band until '95 at the ripe old age of 31) and they're way out of my league...I'm just a pub/club player.

AF

[macpgh]

Oh OK so you know who they are then. I'm a bit out of the mix but they are some old aquaintance of mine. Figured they'd be still playing around & keeping busy. You never know who you may come across while out playing or in jam circles. Are they are still active in the music scene in your part of the world?

I was invited by alvin lee to come over to london to play the marque club a long long time ago

[Ammanford Fats]

To be honest, I only recognised the drummers name so I googled him and found the guitar player as well. I've no idea what they're doing now but if I ever come across them, I'll tell them you said "Hi".

Playing with Alvin Lee...nice one!!!...must have been a great experience.

AF

[macpgh]

It was one of my interesting experiences in life. I first met the guy when he had a band together with tom compton & fuzzy samuels, sort of a situation that wasn't a formal thing, but just a get together to jam & do a couple shows. I forget who compton played with but fuzzy was a rasta bass player & a real showman. He was a session guy that played with everybody back in the day & hendrix too. He gave alvins material a different feel from his approach to bass playing. The other guys along with a guy named micky feat sort of were a neighborhood band thing & they all partied out of alvins & within thats circle of people in that neighborhood.....gilmore & harrison. I guess alvin sold gilmore his estate & house studio he built and gilmore stored all the pink floyd stuff out there in one of the barns...all the stage props & stuff.

I lived in florida for a couple years where I picked up & studied the music as I had met a couple of brothers that were from 50 miles away from where I grew up. Their father was involved in similar work as my own dad, and being that nobody in florida was actually from florida....if you were from the same area before coming to florida then you were good friends on that basis...a piece of home in a strange land...hahahaha
But these 2 twin brothers had a blues club & I sat ring side on the house band & soaked up the music as well as all the main stream touring acts passing thru. SO I got to meet alot of artists along the way as everything was friendly & open. SO not only was it guitar lessons, it was also contacts. Florida was a strange experience because of the tourism aspect and then again alot of individuals would retire to the area & that would include musicians. So I met many ethic artists and originators & heard a few stories along the way about other artists. One of my florida friends was a side man to john lee hooker in the 50's and would tell me stories of riding thru the south under segregation times to play the circuit. I've drank old grand dad whisky with johnny winter. I was fortunate enough to meet the fabulous thunderbirds as they often played my friends club which lead to me meeting stevie vaughan and then I would connect with him here in pittsburgh when he was beyond bigtime. Some of my aquaintances here in pittsburgh were originally from the washington DC area & one guy was the singer for roy buchanan. He had put together a big band with a horn section, and they toured the local & NE circuit for a number of years. His rythmn section was the best and his guitar player was probably the top in the area & was tight with paul reed smith & danny gatton other than roy. They'd tell stories of touring with albert king & how crazy he was. If albert took a disliking to you on the bus, he'd stop the bus & take all your stuff off & leave you on the side of the road in the middle of nowhere traveling between shows. I've been rather fortunate as the cards were dealt on my own strange journey thru life. I have a semi distant cousin that was part of the new york city music scene back in the 60's, and he was in the same circle as jimi hendrix. Hendrix used to rock his first child to sleep when they were all hanging out & doing what they did. That was before he went to london & went big time.

How is the music climate in your part of the world? 20 years ago the people I knew in florida would go to europe to play and it was always like they were big time in the way they were recieved there as they were more like the average everyday small time band here in the local scene. Blues music was more of a niche in the big picture or sometimes slightly more based on region.

I liked a band from somewhere over in england called back door slam. I think they were a bunch of teen age kids playing blues, but they got some good exposure here in the media. And I don't know what happen to them since.