bench re-work amp

[shooter]

moving a head style chassis guts to a combo chassis guts, everything gets flipped 
anyway;
if I swap outer wires on pots, they work properly again?

full wave (CT ground) tube to sand gonna be "close enough" for testing (choke input)?

[VMS]

IMHO no wire swap needed

[sluckey]

moving a head style chassis guts to a combo chassis guts, everything gets flipped 
anyway;
if I swap outer wires on pots, they work properly again?

Say what! You been smokin' the bait again? The wires will stay on the same lugs.

For example, when viewing a Volume pot from the back side (that's the side you don't put a knob on!  ) the lug that is CCW from the wiper will always be the ground lug. Even if you rotate the pot 180°, or flip it upside down, or turn it inside out.

[Papa Jim]

Yeah swap em shooter just like when you rotate your 2 prong ac cords in the wall socket your clocks and everything else operates in reverse because you are opposite out from your home planet .

[shooter]

You been smokin' the bait again

that's the problem, haven't started yet 
ok, just slip the knob 180 

[shooter]

now that I gave up on thought, I got some work done 
hopefully lightin up the AC n early DC soon.

[sluckey]

That resembles the layout I used on my Plexi6V6. PT looks like it came from a Hammond AO-43? You don't have anything connected to the negative terminal of that bridge?

[Papa Jim]

I don't know for sure if it makes any hum difference, but I always do lots of tight twists to my filament wires. 

[sluckey]

I don't know for sure if it makes any hum difference, but I always do lots of tight twists to my filament wires. 

You mean like this...

[Papa Jim]

Nah. I would call those more parallel. I mean like this

[sluckey]

Just kidding. When I built that Plexi6V6 I purposely did the heaters like that just to mess with all the twisted wire disciples.   

[Papa Jim]

I figured so.  Or else your twists were so tight and small they were invisible. 

[shooter]

You don't have anything connected to the negative terminal of that bridge?

using the bridge as a FW, so I only need 2 of the diodes, it's a 30A so I elevated it for cooling 

That resembles the layout I used on my Plexi6V6. PT looks like it came from a Hammond AO-43?

If you need a stout II chassis with labels........ 
Soldering on those old cloth wires, there is a "smell" you get that can't be found ANYWHERE else!
John contacted me, so I'm moving the amp to his combo chassis, so I'm trying to stay true to the original design n layout. 

[Papa Jim]

Hey Shooter....It may be obvious, but I have no idea what you are building, or moving to a combo, unless I missed that part. Is it a Plexi     

[shooter]

no idea what you are building

Ya, a plexi6V6, but no building required, just moving it from a head to a combo, well, some soldering required 

[Papa Jim]

Gotcha. Thanks. It helps if I know what I'm lookin at. 

[shooter]

ok, all the easy stuff is done, just gotta fix the 20 or so opens n hunt up a couple 1.5k that are less than 30yrs old   

[sluckey]

So, what becomes of the old chassis?

[SILVERGUN]

ok, all the easy stuff is done, just gotta fix the 20 or so opens n hunt up a couple 1.5k that are less than 30yrs old   

you're becoming quite the amp builder 

[shooter]

what becomes of the old chassis?

yours if you want it, i'll pay shipping, otherwise........someday 

you're becoming quite the amp builder

more like a kit builder 

[sluckey]

what becomes of the old chassis?

yours if you want it, i'll pay shipping, otherwise........someday 

Yes, I want it. I'll pm you later when I get the mower fixed.

[SILVERGUN]

what becomes of the old chassis?

yours if you want it, i'll pay shipping, otherwise........someday 

Yes, I want it. I'll pm you later when I get the mower fixed.

Hmmmmm....what would he possibly need that for, shooter? 

[John]

what becomes of the old chassis?

yours if you want it, i'll pay shipping, otherwise........someday 

Yes, I want it. I'll pm you later when I get the mower fixed.

Hmmmmm....what would he possibly need that for, shooter? 

Putting it on the mower, maybe.

[shooter]

Hmmmmm....what would he possibly need that for, shooter?

I already got more dust-collectors than I need AND broke mowers, hey, package deal!!!   

[shooter]

did to many J hooks, I need a J 

reminded me of the 'ol days spicing 40 pin ribbon cables 

[PRR]

...when I get the mower fixed.

Hmmmm.... I thought of putting the snow-blower away, but left it ready to go. Don't want to tempt fate.

Enough old snow gone that I can see matted brown leaves, last year's "grass", but no life in it.

Did have a frog in the pond.

[Papa Jim]

Looking good Shooter.

[shooter]

Hmmmm.... I thought of putting the snow-blower away, but left it ready to go. Don't want to tempt fate.

Enough old snow gone that I can see matted brown leaves, last year's "grass", but no life in it.

Did have a frog in the pond.

we must be on the same lat line!
I got the mower out to herd leaves, left the snow-blower out and ready, got lots of peepers in the frog-pond, but the resident snapper turtle has yet to show.

[shooter]

the customer ask for a few Mods;
2nd input jack
Metropoulos Zero loss FX
Remove MV

the FX is pretty straight fwd, only ?, because the MV is coming out, do I need a fixed 1M?? they do show a No-MV hookup, the FX has  grd wire, so guessing technically no, guessing technically the .022uF can go also, but a spare DC blocker can't be bad? but some days technical can be a challenge 

[sluckey]

You don't need a fixed 1M but the .022 cap is very important. It prevents anything on the left side of the cap from interfering with the bootstrap bias on the LTP PI.

[sluckey]

How will you do the second input jack? Just the simple Fender style Hi/Lo jacks? Or will you split the grids (Plexi style) and have a bright channel and a normal channel?

[shooter]

Thank you, didn't know about the cap interaction, I'm not an ltp kinda guy
I took your scrapbook example of the 18w, so ya, split v1, but by the example they operate as a single IN like the plexi6v6 by using the HI jack

[uki]

Looking very good so far ! 

[shooter]

too many old movies with the wife n coffee at the café, so a slow bench day 
front panel and pre tubes 97.8% complete 
herbal tea time 

EDIT:
music n tea were good!, 1 wire n a gatorclip, tommorow

[davidwpack]

Nice! I always build in bigger chassis than I need. I like having the extra space.

[shooter]

 
I got a little travel pillow, fits great in the void 

[shooter]

test day 

1st checks, ohms, no tubes;
Tap A to ground ~300k, slow charge - good
all plates to respective B+ - good
all cathodes to ground - good
OT DCR;
 V4 3 to tap A ~ 180
V5 3 to tap A ~ 205

2nd checks, no tubes, 7K dummy load at tap E
Tap A 465vdc .5vac
Tap B 457vdc 35mVac
Tap C 254vdc 2mVac
Tap D 161vdc 1mVac
Tap E 67vdc .2mVac

bias range -20 to -40
No smoke, No hot parts, No blown fuses, good day 

next: more realistic DL value at Tap A to see if the B+ lands closer to the original 400vdc before I get brave with tubes

research lighted power switch from customer, it's a DPST neon, so 2 sets of 2 contacts.  I'm switching both line n neutral BUT the neon lights as soon as I plug in mains, regardless of ON/OFF condition, otherwise works like a switch should 

[sluckey]

research lighted power switch from customer, it's a DPST neon, so 2 sets of 2 contacts.  I'm switching both line n neutral BUT the neon lights as soon as I plug in mains, regardless of ON/OFF condition, otherwise works like a switch should 

Swap the PT wires and the line wires. I have more info on that switch but that's all you gotta do.

[uki]

Where is the pics ?!!!  Of shine neon lights !!   

[shooter]

as soon as I signed off I plugged in the iron 
switch solved
the math say 400v/.05A = 8k
so my 7k at Tap B gives me 404vdc @60mVac = close enough for tubes, put the bias at -38 for start, tubes in the morn, wife's watching movies and it's been a good day 

[Papa Jim]

Sounds like a real good day. Now that was a lesson in what to do before ever putting the tubes in that everyone should follow.

[shooter]

dynamic test day 

initial;
bias -37.3
V4-3 438     p8 26mV   11.38W
V5-3 438     p8 23mV   10.07W
swapped tubes, values follow tubes
bias -38
V4 440  19.6mV  8.62W
V5 440  23.5mV  10.34W

moved on to signal path, see note to self 
forgot to add wire from mix R's of v1 to V2 in 
V1 works good though 
70mVacrms in ~ 3.6Vacrms out
LUNCHTIME

[shooter]

with the open fixed, she's a rock'n n rollin!!! 

gonna show my fixed bias shortfalls;

bias -38 idle DC 434vdc plate .024A  10.42W 74.4%Pdiss - good
max clean signal at speaker (800hz) 403vdc plate .062A -  24.99W/tube - bad?
15 minutes play, no sparky, no red plates, iron cool, tubes taking fingerprints IF more than 1-2 seconds contact

bias pot is just a "thought" away from full minus (-39)

internal debate;
add a Tap to drop vdc back to 400
tweak bias range toward ~ -42_ish
keep rockin and monitor AVG power over time
 

 

[sluckey]

I'd leave the B+ alone and just drop the bias range resistor down to 180K or 150K. Should allow you to run the tubes cooler.

EDIT... I just realized your running 25W per tube (not total). That's way too much! Gonna kill those 6V6s in no time. Get that bias under control.

[shooter]

25W per tube

that's with a sinwave at near max signal drive, continuous, to be clear, at idle, no signal 10.4W/tube.
but I am at the stops, not middle of bias, so i'll tweak the R to get me more range

[Tony Bones]

I'm looking at the pic in post #33 and I don't see a pair of 1 ohm resistors. How are you measuring PA current?

[sluckey]

I'm looking at the pic in post #33 and I don't see a pair of 1 ohm resistors. How are you measuring PA current?

Directly below the two blue bias caps on the board. Two itty bitty 1Ω/1W black resistors.

[sluckey]

that's with a sine wave at near max signal drive, continuous

I'm aware. But that's still pushing 50W_RMS out of a pair of 6V6s. Even Leo didn't claim that. Seriously, back the sig gen down. Those are NOS mil spec tubes. They can't take that kind of abuse.

[shooter]

swapped the range R to 150k (-25 to -50)
set at -39, yields 442vdc 22mA for 10.34W NO signal.
plugged in, set fluke for min/max, guitar in, no strumming, standby off(?)
settled at 441vdc 19mA
played 10min from full ugly to mild make me smile
MIN 16mA
MAX 63mA
AVG 32mA
441 * 32mA = 14.1W/tube

keep going cooler on bias?

[sluckey]

If those tubes are 14W tubes I'd bias no hotter than 9.8W. But those tubes were packaged in '62 and may only be 12W tubes. In that case, I'd bias no hotter than 8.4W.

But just set it the way you like it and play it. When the tubes die put some JJs in it.