1959 Tweed Bassman Board Build

[plexi50]

I am almost finished building a 1959 Tweed Bassman clone board. I have used all NOS Allen Bradley carbon comps.
For coupling and tone caps i used 1963 Good All .022 & .02 capacitors. .1 Mullard Mustard caps from a Traynor YSR1.
Surprising enough they are all dead on there rated values.
 
The resistors as well are in good value range.  All i need is the 250 pf Molded Mica axial lead treble cap. Super hard to find but i managed and it is on the way to me.

I have a 1968 50 watt Bassman output transformer which is 4 ohm. Don't think i will hear a major difference from the original 2 ohm impedance but time will tell.

The cab is Peavey Classic 410E cab. Funny but it worked out having nearly the exact same dimensions as a tweed bassman cab.
The Peavey cab is 1/4" wider but thats it. Hopefully i will be done in the next month. All these parts are not cheap. I used Doug's yellow cloth 22 gauge wire. I have found no better wire than what Doug has.


Edit: I am scratching the use of the Peavey 410E cabinet. No sense in altering a perfectly good 410 cab. I am thinking of a Tweed Head cab like the ones a guy is selling on ebay.
 

[plexi50]

Bias

[plexi50]

Got Doug's yellow 22 gauge cloth wire this morning. Ordered Saturday. I didn't expect it to arrive that fast, as i ordered it over the weekend.
Well 10' of wire went fast. I was left with 1" of it.  Now i need to order a little more. Surprising just how much wire it takes for a complete build.

[p2pAmps]

Looks great man.  Do yourself a favor and order way more wire than you think you need as you will end up using it somewhere. 

[plexi50]

Do yourself a favor and order way more wire than you think you need as you will end up using it somewhere.

Exactly what i have been thinking the last 4 days.  100' of each color should last me for some time. Not to mention that if Doug runs out of this wire i will regret it later. Most of the cloth wire online is really chessy stuff. Thanks for the compliment. I cant wait to hear it.

[plexi50]

Found some 47pf Erie 1kv Ceramic caps for the PI plate resistors.

[plexi50]

Got the Molded Mica El Menco axial 250pf / 500 volt treble cap today. I bought a bunch of them. They are a little smaller than the originals but good enough for me. Waiting on the 5F6A Chassis to arrive.

Edit: Look where i soldered the treble peak cap on the board! Ha!!!!!!!!!!!

[plexi50]

Treble cap position corrected. That's a first!

[plexi50]

The 5F6A Chassis arrived this morning. I have the board screwed down to the chassis and the transformers in place. I wasn't sure the 1968 Bassman OT would have the same bolt hole spacing but it's dead on. Have to put it to the side for a day but will show the progress of it as it gets built. I used fender short stubby 60's screws to screw the board in place.

[p2pAmps]

Liking your build

[plexi50]

Liking your build

One part at a time. If i had the time i would be finished in about 3-4 hours. But i have other things to take care of.
I got a little more done earlier today. Tonight i'm taking a break/

[plexi50]

What size of self tapping screws do i need to buy from Doug for the (3) Belton preamp tube sockets and (3) 8 pin octal tube sockets?
I want this build to have the best hardware i can find. The hole size in my chassis is 6/32. Will Doug's 6/32 size self tapping screws be a tad wider as they are screwed into the chassis? That's what i need.

[DummyLoad]

What size of self tapping screws do i need to buy from Doug for the (3) Belton preamp tube sockets and (3) 8 pin octal tube sockets?
I want this build to have the best hardware i can find.

what is the ID of the hole?


--pete

[plexi50]

All tube sockets holes are drilled  6/32

[sluckey]

I would use 4-40 x 1/4" with kep nuts for all tube sockets on that chassis. I tap my own 4-40 threads  when I'm working with a blank chassis.

[eleventeen]

Well, looky that. A 60's Bassman output tranny will fit. Never thought of that. I have one of those and 2 Bassman chassis I got in a trade.

[plexi50]

I would use 4-40 x 1/4" with kep nuts for all tube sockets on that chassis. I tap my own 4-40 threads  when I'm working with a blank chassis.

I was hoping to not have to use nuts on screws. So is the 6/32 self taping screw 6/32 at the base of the phillips head?
Also i am thinking a 6/32 head will butt up to close into the preamp socket base.
eleventeen i was really surprised that the holes for the OT were spot on and not a hair off.

[sluckey]

Plus i think a 6/32 head will butt up to close into the preamp socket base.

That's why I use 4-40 on sockets. 6-32 will not fit my Cinch noval sockets.

Since your chassis holes are already drilled your options are kinda limited. Unless--- you rotate the sockets and drill and tap new 4-40 holes. Not something I would do on a chromed steel chassis.

Kep nuts ain't gonna be seen in that crowded tweed chassis. 

[eleventeen]

I predict: you're not going to be happy using 6-32 screws on most 9 pin sockets. You put that all together and it just doesn't sit right; the screws don't sit quite vertical through the chassis...one screw eats up all the tolerance for the other one. The heads are a bit too big, too, unless you get a specific variation of pan-head with a slightly smaller head diameter. Most Chinese 9-pin tube sockets don't have mounting hole clearance for 6-32....I don't know what mfr you are using. Some older US made phenolic or black sockets can pass 6-32 without enlarging the mounting holes. I reco you go for 4-40, I think you'll end up a lot happier with the finished product and it will go together with much less  grief.

[Willabe]

I want this build to have the best hardware i can find.

I would use 4-40 x 1/4" with kep nuts for all tube sockets on that chassis.

Sluckey's suggestion is the finest hardware in this case. Only step up would be the same but stainless steel. 

[DummyLoad]

run with 4-40 for the 9 pin and 6-32 for the octal. you can use 4-40 for the octal, but 6-32 hardware fits better. use 1/4" with a keps nut. i use stainless for just about all my builds.


loose fit or close fit 6-32 hole? why asked what the actual hole diameter is. if the hole was drilled for loose or close fit BOLT, then to install a self-threading screw, you'd need to use self tapping screw that fits and cuts thread. assume the hole was drilled @ .149" for 6/32 bolt, then you'd need to use a #10 self tapping screw to cut thread with type A, AB, B, or 25 self tapping screw - see chart below.


http://www.shender4.com/thread_chart.htm   <---- for machine screws


http://www.ebninc.com/technical/screws-self-tap.pdf    <---- for self tapping screws


--pete

[Jack_Hester]

This guy has a large selection of stainless hardware, at cheap prices: 

http://stores.ebay.com/Albany-County-Fasteners?_rdc=1

Jack

[plexi50]

Great replies. I will go with the 4-40 (was thinking MOPAR) for a minute here. 4-40 for the preamp & 6/32 for the octals.
More later. Much thank all!

[eleventeen]

Good decision. What you said earlier----that 6-32 screw heads are a bit too big and will impinge on the area they go in when mounting 9-pin sockets---it is very true. I don't know what the particular head type Fender used on their screws is called. It is smaller diameter than nominal pan head but larger than filister head. "Modified pan head?"


I can tell you, you'll completely hate life if you try to use 6-32 on a chassis where you cut/drill the holes. The big hole and the two small holes have to be made with better than NASA-grade precision or they will simply not sit properly, and even then....... The heads interfere with the tube sockets, the screws pull against each other, it's a mess. And to gain what? A 4-40 screw is only 20 times stronger than it needs to be to secure the tube and socket under any imaginable conditions versus 50 times stronger as a 6-32 would be? Save yourself the grief.

[plexi50]

I ordered 12 of each. 4-40 with kep nut and 6/32 with kep nut.  Also 2 Carling switches. I am using Marshall tube sockets instead of the fender type. Those Marshall sockets really grab power tube pins good. I just don't like the new fender sockets. Retention a few time and the pins break off. Maybe there is a good Fender socket someone could recommend before i commit to using what i have?

[Willabe]

I am using Marshall tube sockets instead of the fender type. Those Marshall sockets really grab power tube pins good.

Which 1's?

Got a picture/description/company model #?

[plexi50]

I am using Marshall tube sockets instead of the fender type. Those Marshall sockets really grab power tube pins good.

Which 1's?

Got a picture/description/company model #?

The Belton socket pictured.

[Willabe]

Oh, Ok, thank's. 

[plexi50]

Today progress. I'm tired/

[plexi50]

More/

[plexi50]

I went to the ACE hardware store and found the 4-40 preamp socket screws & 6/32 octal socket screws. I just had to get those sockets mounted so i could get some work out of the way. The 4-40 screws with nut are perfect! Everything went pretty smooth.The worst part is yet to come.  I actually dread heater filament wiring. It's not as bad as it used to be for me to do but i still hate the getting the wiring exact looking on all sockets.  I simply (Hate) heater filament wiring. Give me a chassis run over by a truck and i am happier.

[Willabe]

Looking great!

Oooo, next the dreaded heaters.            

[HotBluePlates]

I always lay in heaters first on a tweed chassis; last on a blackface chassis.

[plexi50]

I don't have any green heater wire. I feel better now. I will order some from Doug now.
I decided to put a switchcraft jack between the (4) RCA speaker out connectors.

[plexi50]

Power transformer from a 1962 Wurlitzer Organ. 360-0-360. Not sure i will keep it in the amp. I was shooting for 325-0-325 for the original Tweed Bassman B+ of 400 VDC on the power tube plates. Will see/

[TIMBO]

Nice work Plexi.
I have a chassis similar to yours, just a bit smaller. I gutted it for parts and was going to chuck it as the layout was not great.
I held onto it just in case. Not looking forward to squeezing a board into it.

[HotBluePlates]

Power transformer from a 1962 Wurlitzer Organ. 360-0-360. ... I was shooting for 325-0-325 for the original Tweed Bassman B+ of 400 VDC on the power tube plates. ...

I believe you'll have over 450vdc loaded, and a tad over 500vdc unloaded.

[plexi50]

Power transformer from a 1962 Wurlitzer Organ. 360-0-360. ... I was shooting for 325-0-325 for the original Tweed Bassman B+ of 400 VDC on the power tube plates. ...

I believe you'll have over 450vdc loaded, and a tad over 500vdc unloaded.

Yeah i know it's not the right PT for this.
I am just going to spring out in the morning,load my visa and buy the right PT for it. I have come this far and i don't want to skimp and wind up with a Tweed Ampeg. The PT has been removed/

[plexi50]

I got the advertised 325-0-325 PT this morning. Unloaded i decided to check the HV A/C recto leads and i am getting, Edit 340-0-340. Will see what it winds up being after it is under load.  I should be seeing 325-0-325 on my DVM.  I am almost ready to flip the switch and hear good stuff. But i  ran a foot short on the heater wire i had got from Doug.  Ordered more and it will be here friday.  All in all the hard work is finished minus 12" of heater wire from the PI pins 4&5 to the octals and lamp.

NOS Sylvania preamp 12AX7A tubes. NOS 1958 5U4GB for now. Bogen 6L6GC power tubes for now.

[plexi50]

I also need to take a 1968 Fender doghouse to a machine shop and get it shortened up by a few inches. Width and screw hole spacing is spot on. Length is over sized a bit.

[plexi50]

Oh i almost forgot the NOS 12AY7 V1 tube. Have 12ax7's in my mind and over looked that.

[plexi50]

Finished heater wiring and fired it up. Sounds pretty darn good. Checked bias and plate voltage. Stone quiet amp at idle.
Plate voltage after 30 minutes is steady at 419VDC. Bias in grid volts is -53 VDC.  Schematic says -48. I am using a 5U4GB rectifier seeing as i used the last GZ34 i had earlier this week on another amp. The V1 cathode voltage is as the schematic at 2.500 volts. I will post the voltages later on the valve voltage page after i get another GZ34 and do some comparisons in tone and voltages. I am very satisfied as to the entire build process. It went smoother than i expected. I'm sort of burned out building amps. After i built the board i was basically committed to find the chassis and go for it.
More later/

[plexi50]

Final/   

[HotBluePlates]

Great job all around!!

[plexi50]

Thanks HBP! I have been wanting to do this particular build for years but always got side tracked.
Remember that 1955 Bassman i found for pennies? That got me started on my Tweed kick.

[sluckey]

Really looks good! That would make a nice plexi conversion! 

[plexi50]

Really looks good! That would make a nice plexi conversion! 

If i had my way i would get bed sheets and T shirts with the 5F6A print on them.  No socks though. 

Bigger Pic's / http://triodeamplification.com/5F6A.HTML
 

[plexi50]

Got the 1968 Super Reverb Doghouse pan shortened up back from the metal shop today. Have to do a few little cosmetic finishing touches but it fits perfectly. Have it wired through rubber bushing and mounted. This is as close to the real thing as i am ever going to own.  Waiting on those 1959 Tungsol 5881 tubes.

[DummyLoad]

very nice build. congrats.

--pete

[plexi50]

I think i have some OCD going on here. Selenium rectifier.