Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: shooter on April 15, 2019, 12:54:56 pm
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moving a head style chassis guts to a combo chassis guts, everything gets flipped :think1:
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)?
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IMHO no wire swap needed
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moving a head style chassis guts to a combo chassis guts, everything gets flipped :think1:
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! :icon_biggrin: ) 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.
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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 :laugh:.
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You been smokin' the bait again
that's the problem, haven't started yet :icon_biggrin:
ok, just slip the knob 180 :think1:
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now that I gave up on thought, I got some work done :icon_biggrin:
hopefully lightin up the AC n early DC soon.
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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?
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I don't know for sure if it makes any hum difference, but I always do lots of tight twists to my filament wires. :dontknow:
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I don't know for sure if it makes any hum difference, but I always do lots of tight twists to my filament wires. :dontknow:
You mean like this...
(http://sluckeyamps.com/6v6plexi/P-6V6_04.jpg)
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Nah. I would call those more parallel. I mean like this
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Just kidding. When I built that Plexi6V6 I purposely did the heaters like that just to mess with all the twisted wire disciples. :icon_biggrin:
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I figured so. :icon_biggrin: Or else your twists were so tight and small they were invisible. :laugh:
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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 :laugh:
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........ :icon_biggrin:
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. :occasion14:
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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 :w2: :dontknow: :help:
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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 :icon_biggrin:
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Gotcha. Thanks. It helps if I know what I'm lookin at. :laugh:
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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 :think1: :icon_biggrin:
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So, what becomes of the old chassis?
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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 :think1: :icon_biggrin:
you're becoming quite the amp builder :laugh:
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what becomes of the old chassis?
yours if you want it, i'll pay shipping, otherwise........someday :think1:
you're becoming quite the amp builder
:l2:
more like a kit builder :icon_biggrin:
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what becomes of the old chassis?
yours if you want it, i'll pay shipping, otherwise........someday :think1:
Yes, I want it. I'll pm you later when I get the mower fixed.
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what becomes of the old chassis?
yours if you want it, i'll pay shipping, otherwise........someday :think1:
Yes, I want it. I'll pm you later when I get the mower fixed.
Hmmmmm....what would he possibly need that for, shooter? :dontknow:
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what becomes of the old chassis?
yours if you want it, i'll pay shipping, otherwise........someday :think1:
Yes, I want it. I'll pm you later when I get the mower fixed.
Hmmmmm....what would he possibly need that for, shooter? :dontknow:
Putting it on the mower, maybe.
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Hmmmmm....what would he possibly need that for, shooter?
:dontknow:
I already got more dust-collectors than I need AND broke mowers, hey, package deal!!! :icon_biggrin:
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did to many J hooks, I need a J :icon_biggrin:
reminded me of the 'ol days spicing 40 pin ribbon cables :think1:
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...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.
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Looking good Shooter.
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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.
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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 :icon_biggrin:
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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.
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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?
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Thank you, didn't know about the cap interaction, I'm not an ltp kinda guy :laugh:
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
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Looking very good so far ! :m11
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too many old movies with the wife n coffee at the café, so a slow bench day :icon_biggrin:
front panel and pre tubes 97.8% complete :laugh:
herbal tea time :icon_biggrin:
EDIT:
music n tea were good!, 1 wire n a gatorclip, tommorow
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Nice! I always build in bigger chassis than I need. I like having the extra space.
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:laugh:
I got a little travel pillow, fits great in the void :icon_biggrin:
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test day :w2:
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 :icon_biggrin:
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 :dontknow:
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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 :dontknow:
Swap the PT wires and the line wires. I have more info on that switch but that's all you gotta do.
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Where is the pics ?!!! Of shine neon lights !! :think1:
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as soon as I signed off I plugged in the iron :think1:
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 :icon_biggrin:
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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.
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dynamic test day :w2: :w2:
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 :think1:
forgot to add wire from mix R's of v1 to V2 in :BangHead:
V1 works good though :laugh:
70mVacrms in ~ 3.6Vacrms out
LUNCHTIME
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with the open fixed, she's a rock'n n rollin!!! :guitar1
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
:dontknow:
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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.
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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
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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?
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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.
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that's with a sine wave at near max signal drive, continuous
I'm aware. But that's still pushing 50WRMS 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.
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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?
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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. :icon_biggrin:
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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.
:thumbsup: I didn't recognize them as resistors.
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going cooler, it's not my rig :icon_biggrin:
If it was mine it woulda been '34s self biased :icon_biggrin:
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After 3hrs, I’m more convinced fixed bias makes no sense to me :think1:
Idle NO signal
V5 446vdc 18mA 8.03W
V4 446vdc 13mA 6.10W
10 minute dynamic testing (V5 reference measurments)
(math Max V * Min I, Avg V * Avg I, Min V * Max I)
Min power 447vdc * .016A = 7.2W
Avg power 438vdc * .034A = 14.9W
Max power 411vdc * .068A = 27.9W
The problem I see using the min/max/avg, I have no clue how the data points shake out
Ie; 90% data =< avg?, or avg = just 1 max data and 1 min data?
All that said, the amp sound like it “should” to my Go/No_Go ears. All the things the knobs control seem to change as expected, nothing smells outta the ordinary, (my favorite test :icon_biggrin: ).
On to the FX loop, final voltage checks.
Greatly appreciate the opportunity to do this build, and all the support I got in the process.
dave
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Pam got home from a 12hr before I finished soldering, so guitar Monday.
I dropped the D & E taps from +33~ to -4 from original Tap volts. Left the PI +32v now 302vdc, 205 at plate.
need to tie in the FX B+ tap at C but I don't want to fly it that far, so thinkin.
the original build had the teal solder standoff up front, the new chassis is 1/2" higher, so after exhaustive standoff egg hunt, settled on a dab of superglue, cross thread the standoffs n call it a day :icon_biggrin:
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> Min power 447vdc * .016A = 7.2W
> Max power 411vdc * .068A = 27.9W
A fix-bias amp idles cool when no load power is demanded. When working hard in a load the current rises, but some of the increased power goes to the load, does not heat the tubes.
I have NO idea what this amp is. 6V6? Two? 0.016 per tube or per pair?
Two 6V6 at OVER-voltage (>400V is a LOT for 6V6) "can" suck 2*28W= 56 Watts from power supply, and pass maybe 25 Watts to the load, leaving 31W/pair or 16W in each tube. This is hot for a 14W tube. But how long can your fingers keep it up? It may be fine. It may not be.
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V5 446vdc 18mA 8.03W
V4 446vdc 13mA 6.10W
How hot temperature does it run?
Maybe you are interested in this info about bias balance:
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does not heat the tubes.
Thanks PRR, ya 6V6, once I dialed it back to the current #'s I could play full roar 10min and NOT leave fingerprints on the top of tube, sides might take some skin if you're not quick.
thanks UKI, it's gonna be the 1st 80degree day here AND sunny! so i'll try and watch tonight becasue I'm dragging the cab to the porch and playing till the neighbors start shooting :icon_biggrin:
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thanks UKI, it's gonna be the 1st 80degree day here ..
Oh I was talking about the tubes, in those videos the guy shows how hot the tubes are while unbalanced, 400° one side and way less in the other 260° ish, after balancing the cothode current, both tubes doing about 270°ish. Runs way cooler !!
V5 446vdc 18mA 8.03W
V4 446vdc 13mA 6.10W
Getting it around 15.5mA each tube it would do 7W ish each sides!
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thanks Uki, imbalance in tubes has been going on before I could solder :icon_biggrin:
I will note it with the customer. My guess, in time those really pretty NOS tubes will be swapped out for new skol, but, she sounds quite nice the way it sits.
I had to test-drive since dropping the pre volts, even to my non musical ears THAT change brought back some "magic sauce" lacking at the higher volts. Before I couldn't dial the gain pots as far, my guitar volume controlled less than expected. Now, once I set the gain pots and TS, all I gotta do is play with my guitar for compete "range" control.
the only downside, Mama's china dishes come close to jumpin outta the cabnit :icon_biggrin:
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...it's gonna be the 1st 80degree day here AND sunny! so i'll try and watch tonight becasue I'm dragging the cab to the porch and playing till the neighbors start shooting :icon_biggrin:
:huh: :l2:
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finished the FX, tested only using patch cord out back in, other than a small POP when I engaged didn't notice any signal change. played her for about 1/2hr straight, no bullets!!, no smoke, no smells, shipit!
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So, what's the rest of the story?
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UPS said it made it on the 1st
much as I know, hopefully it's too good to put guitar down :l2: :dontknow:
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I checked email n found this;
Incredible job on the amp, it really sounds great!
Thanks so much for taking this on!
thanks to all
dave