Starting my 5F6A Hoffman build

[pompeiisneaks]

Here are some initial shots.  Coming along nicely.

https://goo.gl/photos/5VLYdHztRaMJHN5V8

~Phil

[pompeiisneaks]

sigh, there's always something.  I tried first power on and blew the 3A fuse.  I didn't yet have a rectifier tube in, and was slowly bringing it up on the variac and got to 12v when it blew the fuse.  I then put my ammeter in series between the input of the fuse and the power switch and slowly brought it up and its getting maybe 35mA until I hit about 5 or 6 volts and then it jumps to 6A so I shut it off.  I'm guessing I've got one of my leads touching somewhere it shouldn't in the power chain.  I'll try that out tomorrow night, but don't have time tonight to look (this was all done yesterday when I finished the build).

~Phil

[pompeiisneaks]

Okay, so this makes no sense.  Now I can't get the issue to reproduce, I just don't want to throw in another 3A fuse and have it blow again.  Is it wrong to run power into the amp with no rectifier in?  Does that just cause current to run hot to ground? 

I have tested the resistance and grounding on t his amp and identically on my EH-185 that I just used and both are brand new identical transformers, and both show the exact same readings for resistance on the coil. 

I get about 70 mA now at say 12 volts, and as i raise the voltage up on the variac, it slowly climbs in amps as I'd expect.  Why was I jumping so high to 5 or 6 amps when it blew that fuse at first? 

This is a brand new transformer from Doug, in a brand new amp without even the rectifier tube connected. 

~Phil

[Paul1453]

There should be no problem powering up without the rectifier, and all other tubes in.

Current cannot flow in an open circuit.

If current is flowing there has to be a path for it, and with all the tubes out there really shouldn't be one for it to take.   

If the rectifier tube is out, standby switch open, then there are only a few places current could flow through faulty components.

Your 6.3VAC may be shorted somewhere.
if that .05 600V cap on the 5VAC was short that may do it.
Or something in the bias circuit is shorted.

[pompeiisneaks]

Oh, I'll have to check the bias circuit. 

The Hoffman 5F6A doesn't have that cap, so that wouldn't be it.  I may just temporarily desolder the bias and see if it is 'gone' and go from there. 

This was my first power on, so I had 0 tubes in, I wanted to first make sure something like this couldn't cook the rectifier. :)

Thanks for the pointers.

~Phil

[Paul1453]

It would be easier on your PT if your 5 or 6.3 wiring was shorted by a solder blob or something.

Those windings can both stand more abuse than your HV winding which the bias tap also comes off.

Your HV winding will end up being destroyed by excess current flow much quicker than the other 2 windings. 

You don't want to kill your PT. 

[sluckey]

I suggest you quit using that variac to slowly bring up a new build amp. Instead, use a simple lamp limiter. It will tell you if you have excessive current flow (short) and also prevent fuses from blowing. You should also consider fuses as the most disposable component in an amp. Keep plenty on hand.

If you are not familiar with a lamp limiter or how to use one, look here...

     http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

[Willabe]

It would be easier on your PT if your 5 or 6.3 wiring was shorted by a solder blob or something.

Those windings can both stand more abuse than your HV winding which the bias tap also comes off.

Your HV winding will end up being destroyed by excess current flow much quicker than the other 2 windings. 

Why?

A short is a short. A winding is just a coil of wire a 10A wind will burn up just like a 100mA wind if shorted.   

[pompeiisneaks]

I suggest you quit using that variac to slowly bring up a new build amp. Instead, use a simple lamp limiter. It will tell you if you have excessive current flow (short) and also prevent fuses from blowing. You should also consider fuses as the most disposable component in an amp. Keep plenty on hand.

If you are not familiar with a lamp limiter or how to use one, look here...

     http://sluckeyamps.com/misc/Amp_Scrapbook.pdf

I built one, I've just been using the variac because I thought it was supposed to be better.  I may have to look for a better source for fuses then, because Doug's are .80 per and locally its more like 1.20 per.  If I blow through a few of them, it adds up pretty quickly :) (on the Vox AC100 I found out I was using fast blow and that was why they were blowing, about every 5th power on I'd lose one, I went through 10 bucks in fuses or more on that build... it adds up, of course that was mostly my fault for buying the wrong kind but... yeah).

I'll try the bulb limiter.  I got wary of it because the vox, while working, seemed to always have the bulb on anyway (is that because its a 100W amp, and I had a 100W bulb? I'm not sure how the thing works really).

~Phil

[Paul1453]

It would be easier on your PT if your 5 or 6.3 wiring was shorted by a solder blob or something.

Those windings can both stand more abuse than your HV winding which the bias tap also comes off.

Your HV winding will end up being destroyed by excess current flow much quicker than the other 2 windings. 

Why?

A short is a short. A winding is just a coil of wire a 10A wind will burn up just like a 100mA wind if shorted.

Yes that is true, but the thin 100 mA wire will burn up like 100 times quicker than the thick 10A winding.

The thinner wire used on the low current/high voltage winding will not stand the abuse nearly as long before it is destroyed. 

As one who has abused a few PT's myself, I noticed that those thicker windings were more tolerant of my nonsense than the HV tap.

In cases of extreme abuse, that wire winding becomes like another fuse.  The thicker the wire, the more it can take before it pops.   

[eleventeen]

Yeah, fuses ain't cheap. And you very very rarely blow just one. Like potato chips.


One thing I have done and it's obviously not incredibly safe but it definitely does not have to be dangerous if you "take measures"; is to find some old shielded wire and get some of the teensy strands of wire out the braided shield. Get a small junky terminal strip and solder just one of those strands across two terminals, then feed your AC thru that bridge for your tests. Mount on a block of wood.


How do you know how much current will blow that "fuse"? You say you have an AC ammeter. I don't, at least not one I would use eg; a multimeter and I am genetically programmed not to measure current through a multimeter. But if you have your variac and your AC ammeter, you can determine the blow point of such a "fuse" rather easily. Just plug any old (working) anything into the AC outlet of your hillbilly fuse deal and while monitoring your AC ammeter, crank your variac until it melts. If the ampacity is too low, use two strands.

AND if you blow a fuse and have to resolder in another 1" piece of teeny wire, obviously unplug the whole thing. It would be nice to use an IEC AC inlet connector (instead of an AC cor leading off "somewhere" because then you see right in front of your face that it is plugged in.

As for the fairly dangerous terminal strip and the shock hazard; don't leave it plugged in and put the terminal strip under a jar. That's the way we did it in the old days AND WE LIKED IT!

[pompeiisneaks]

Lol nice. 

I'm using my fluke 117 DMM as the ammeter, but I'm using an aligator clip on the input of the fuse and the point tip of the red side connecting to the other side of the area I'm opening.  I touch it briefly, see the reading, adn can basically pull it off immediately.  As stated I initially was getting about 40mA and then when I rolled past something like 5V it would jump to 5 or 6A and I'd pull it off.  The  last round of testing I couldn't get it to do it, and all seems fine, so I'm boggled...  I'm going to use the bulb limiter after I buy a few more 3A slow blows.  (As Steve said, I shouldn't blow the fuse anyway, if the bulb lights up, it saves me a fuse).

~Phil

[sluckey]

For the kind of money you're blowing on fuses, you could buy an assortment of circuit breakers from Weber! Probably a good idea. You can even permanently install in an amp. My Sunn Sceptre had a circuit breaker rather than a fuse. Most all TVs from the '60s had a circuit breaker rather than a fuse.

     http://www.tedweber.com/amps/fuses-circuit-breakers

I'll try the bulb limiter.  I got wary of it because the vox, while working, seemed to always have the bulb on anyway (is that because its a 100W amp, and I had a 100W bulb? I'm not sure how the thing works really).

That's how it's supposed to work, unless you've watched that usless Uncle Doug video. A 100W bulb pulls .83A from a 120V wall outlet. That is the absolute max current that can flow thru the limiter even if the amp that's plugged in has a dead short across the power cord. A properly working 100W amp plugged into a 100W lamp limiter will cause the lamp to glow at a very reduced brightness. If the amp has a dead short the lamp bulb will glow at full brightness.

For a 50 watt amp I'd use a 75 watt bulb if I had one. Since I don't have one but do have lot's of 90 watt bulbs, that's what I would use. A 90 watt bulb will limit the maximum current flow to 0.75 amps.

There's nothing bad about using the variac on a new build. I use one to set the line voltage to 120VAC before I take voltage readings to put on my schematics. In the future when I'm checking voltage readings I use the variac to set the line to 120VAC. Then my voltage readings should agree with the readings on my schematic. I also use a variac to slowly bring up old amps such as the Hammond organ amps I work on. Bringing it up slowly allows me to assess the condition of the old filter caps and to also attempt to rejuvenate them. I do have other uses for a variac...

...But I don't use a variac to slowly bring up a new amp. Doing so is just a waste of time IMO and just adds useless voltage readings and maybe confusion. And they don't prevent fuses from blowing!  The lamp limiter is much more useful to me. If the lamp glows full brightness, I know there is a short (probably in the mains circuit) that needs my attention. If the lamp glows pretty bright, I will suspect a short on the secondary side of the PT. If the lamp briefly glows kinda bright then settles down to a low glow, I assume the amp has no shorts. At that time, I remove the lamp limiter and put it back into storage. It's job is done for that amp. And no fuses were harmed.

[pompeiisneaks]

Excellent info, thanks!

I'll take that and do some tinkering tonight.

~Phil

[sluckey]

While tinkering, use some working amps and some different size bulbs to get a feel for what's normal.

[pompeiisneaks]

I have the EH-185 and the bulb is a 72 watt actually.  It lights up quite bright on it, but works a charm. 

The bassman now seems to be 'working'  it has a very dim light up on first power up, and hten when I flip standby it brightens up quite a bit for a split second then goes back to a dull glow.  I then tried it off the bulb tester and it didn't blow the fuse and seems to be okay.  I put in the speaker instead of the dummy load and put the guitar in and its making quite a racket.  A sort of high pitched hum (Is that 120 cycle hum?) and if I have the presence down to 0 it makes a horrific noise, (with volume at 0) and it mostly goes away except that high pitched hum afterwards.  I could play a tiny bit of guitar but it sounds horrid.  I also checked the mV on both 1 ohm resistors and it was pretty high at idle, somewhere around 140mV or so, sometimes spiking higher, not sure why other than maybe the noise it was making was causing a load on them.  I tried dialing the bias pot down and got it to about 120-110mV or so I think, is that in the ballpark?  It seems from the datasheet at around 350 v (I don't recall if my voltage was that, but I know this amp is supposed to be around that, I'll have to get some measurements maybe tomorrow.) that it should be 132 mA for fixed bias.

soi is the high pitched squeal due to having the OT wired backwards on the power tubes? How do you know which is right?  (Just try and fail? and fix?)


I'll try that anyway, but just thought I'd report with what I'm finding.

~Phil

[pompeiisneaks]

Okay, that was it, the OT were reversed... Again, how do you know ?  Or is it just random, and is that only a problem with NFB?  I've never encountered it but my other builds didn't have NFB. 

Sounds pretty damn loud I'll tell you what.  It seems a bit overly crunchy at max volume with presense at max (That reducest he amount of NFB right?) 

About where should I put my idle current at?  Closer to the 132mA of the datasheet or is that max?

~Phil

[sluckey]

Okay, that was it, the OT were reversed... Again, how do you know ?  Or is it just random, and is that only a problem with NFB?

You don't know. It's not random, but the manufacturers usually don't give enough info on the PT phasing to be able to absolutely work it out on paper. Just consider it a 50/50 coin toss. If it's right that's great. If not, swap the primary leads. Always leave the primary leads uncut until you know for sure which is correct.

About where should I put my idle current at?  Closer to the 132mA of the datasheet or is that max?

132mA??? I don't know what that refers to. I would initially set the bias pot to provide maximum negative voltage on pin five of the output tubes. Then decrease the bias voltage to give 70% idle dissipation. You'll need to measure plate voltage and cathode current to calculate static dissipation.

Read this easy to understand info about biasing an amp...

     http://www.duncanamps.com/technical/lvbias.html

[sluckey]

I put in the speaker instead of the dummy load and put the guitar in and its making quite a racket.  A sort of high pitched hum (Is that 120 cycle hum?) and if I have the presence down to 0 it makes a horrific noise, (with volume at 0) and it mostly goes away except that high pitched hum afterwards.

This kind of problem is one example why I never power up an amp for the first time using a dummy load. Being able to hear what's going on is just as important as any voltage reading you would make at first turn on. Having a howl/squeal NFB problem can quickly damage OT, output tubes, etc. if allowed to continue for a length of time. Having a speaker connected will immediately alert you to that problem. You don't have to wait to see your plates going cherry to know that something is not right.

[pompeiisneaks]

Okay, that was it, the OT were reversed... Again, how do you know ?  Or is it just random, and is that only a problem with NFB?

You don't know. It's not random, but the manufacturers usually don't give enough info on the PT phasing to be able to absolutely work it out on paper. Just consider it a 50/50 coin toss. If it's right that's great. If not, swap the primary leads. Always leave the primary leads uncut until you know for sure which is correct.

About where should I put my idle current at?  Closer to the 132mA of the datasheet or is that max?

132mA??? I don't know what that refers to. I would initially set the bias pot to provide maximum negative voltage on pin five of the output tubes. Then decrease the bias voltage to give 70% idle dissipation. You'll need to measure plate voltage and cathode current to calculate static dissipation.

Read this easy to understand info about biasing an amp...

     http://www.duncanamps.com/technical/lvbias.html

I think I get biasing pretty well, (but I'll still read that link just to be sure) I was getting ~120mV on my 1 ohm resistors to ground which in theory means about 120mA idle plate current.  In looking at the datasheets they say that 132 mA is the plate current expected, but I don 't know if that's 70% or what.  (Attaching screenshot with red highlighting). 

I thought measuring based off the bias voltage is less accurate than using the 1 ohm to ground method (Or are you just telling me to set that to the max negative as a starting point and then adjust up to the right current?)

That's also excellent info about using the speaker first and not a dummy load, I'll start doing that from now on. 

Thanks,

~Phil

[sluckey]

I think I get biasing pretty well, (but I'll still read that link just to be sure) I was getting ~120mV on my 1 ohm resistors to ground which in theory means about 120mA idle plate current.  In looking at the datasheets they say that 132 mA is the plate current expected, but I don 't know if that's 70% or what.  (Attaching screenshot with red highlighting).

It's important to understand this and get the bias set right, especially in a fixed bias amp. Cathode bias (aka self bias) is more forgiving because the hotter the tube runs, the higher the bias voltage goes. Kinda like an old air cooled VW Beetle, the faster you run, the cooler the engine. But fixed bias will not dynamically change. If there is a failure in the bias supply, or even if you just set it wrong, it will happily let your tubes melt, and possibly burn other expensive components.

Looking at your data, that 132mA number is for max signal conditions. When setting the bias, you will be setting up with zero signal conditions, so use 88mA. But more importantly... Those numbers are for TWO TUBES! Did you miss that note? So, really you would be looking for about 44mA if your plate voltage is 360V. That would yield a safe 15.8 watts. But you had 120mA and I bet your plate voltage was more like 400V. That would yield about 48 watts and will quickly destroy your tubes and maybe damage your OT as well.

I suggested "I would initially set the bias pot to provide maximum negative voltage on pin five of the output tubes." That's just a preliminary caution to avoid destroying anything for a first time power up. IMO, that's just as important as connecting a speaker. You really want to use all your senses... sight, sound, smell, taste (not really!), and touch. Learn to rely on those senses as well as any meter readings. They are usually quicker than fumbling with a meter switch and probes.

[pompeiisneaks]

ahh gotcha.  I also need to double check voltages, because it may be more like 400.  The PT does 354-0-354 pre rectifier, but I'm not sure how that comes out the other side, it may be about 400 instead of the 350 I was stating. (I think I recall something in the past talking about a rectifier output is some multiple, and the solid state ones are even more efficient like 1.5x maybe its 1.2 or 1.3 depending on the rectifier tube?) I'll double check those voltages as well tonight. 

~Phil

[HotBluePlates]

ahh gotcha.  I also need to double check voltages, because it may be more like 400.  ...

Sluckey said, "So, really you would be looking for about 44mA if your plate voltage is 360V" but you should also know that's valid if your screen voltage is also 270vdc as in the data sheet condition.

Your idle plate dissipation target may be determined by the plate voltage you have. However, the plate current which will actually flow will be determined by the screen voltage and bias voltage. So if you're trying to cop a data sheet's condition, you need to be very mindful of those numbers.

... The PT does 354-0-354 pre rectifier, but I'm not sure how that comes out the other side, it may be about 400 instead of the 350 I was stating. (I think I recall something in the past talking about a rectifier output is some multiple, and the solid state ones are even more efficient like 1.5x maybe its 1.2 or 1.3 depending on the rectifier tube?) ...

354-0-354 (which sounds like an unloaded voltage measurement) could be as high as 354v*1.414 = 500vdc rectified (again, probably unloaded). The "1.414" is √2 and is the factor for converting RMS of a sine wave to a peak voltage. If no current is drawn, the filter cap will charge to the peak of the incoming voltage.

Even if you have a solid-state rectifier, that voltage (at the 1st filter cap) should come down once you plug tubes in and draw some current off the supply. That's because the PT has winding resistance.

The other factors for different rectifier tubes (1.3, 1.2, 1.1) are only estimates based on observing particular amps which use those rectifiers. The exact voltage drop from the RMS*√2 peak voltage depends on the size of the 1st filter cap, how much current the circuit draws, the internal resistance of the rectifier and the PT winding resistance (plus any added resistance between the PT winding & rectifier plates). Without knowing all that stuff, there's no easy way to guess what the resulting dc voltage will be, other than those observations I mentioned earlier.

And how hot your bias your tubes will change the current draw of the amp (at least at idle), which will change the voltage at the output tube plates (and, to a lesser extent, probably the overall voltage of the power supply).

[pompeiisneaks]

Thanks, that helps.  I look forward to having this stuff all just in my head like it is for you guys :)

~Phil

[Willabe]

I think I get biasing pretty well, (but I'll still read that link just to be sure)

You really need to read that link 1st before you do any more.

Your cooking those tubes at 132mA, 120mA.   

[pompeiisneaks]

I've not turned it back on since I was told that. I'll check into what's going on, but that almost makes me think I'll need to change that bias resistor to lower the current (raise the voltage = raises the resistance right?  That lowers plate current?)

I'll play with that when I do get time to turn it back on etc.

~Phil

[sluckey]

Just pull the output tubes, plug it directly into the wall socket, turn it on, and measure the voltage on pin 5 of each output tube socket with the bias pot set fully CCW. Then crank the bias pot max CW. What readings do you get? Actually this will be 4 readings, two readings per tube.

[pompeiisneaks]

I did so this morning, and CCW and CW had almost the same readings, about 215 mV.  I couldn't get it to stay solid though, it seemed to go all over the place.  I decided to quickly put them back in and for only a short time  test it and I was getting readings ALL over the place, 20mV, 110mV 200mV etc.  I don't know tons about the NFB part, but I have that connected to my 2 ohm tap that's connected to the rca's in parallel (with no speakers yet attached) and I have a separate normal speaker jack connected to the 8 ohm tap and that's waht I've been using for testing the output.  When I dialed down the presence to 0 and all the other pots, as well as removing the guitar jack (I wasn't playing it, I had it connected is all).  The values all of a sudden came in just fine.  I can't recall now w hich one I had, but my low end was at -65.6 V on bias, 31mV on one tube and 26mV on the other, and all the other way it came out -62.6V on bias and 53.7mV on left, 51.4 mV on  right tube.  I then dialed that down to about 40mV (as you said I should be close to 44mV/mA but now that I've done that, I realize I wasn't looking at my voltages either, let me go double check those as well, I may want to tune it just a touch more if the voltages are higher. 

Ultimately, though, it now sounds really nice, I think I had some really weird values coming in through the NFB maybe?  or some other unexplainable reason that just 'went away' after the amp was up and warm etc? 

Ideas on why it was all over the place?

~Phil

[pompeiisneaks]

Okay sorry, voltages on plate and grid are 455 on both tubes.  If I then look at the datasheet for 450V I see 116 for two tubes or 58mA for each tube.  On those sheets, that's the good operational (70%) value right, they're giving you operational values, not the max for the tube?  So if that's the case, I can go up to 58mA instead of the 40ish I've got now? 

Just want to make sure before I set it too hot.

~Phil

[sluckey]

Just pull the output tubes, plug it directly into the wall socket, turn it on, and measure the voltage on pin 5 of each output tube socket with the bias pot set fully CCW. Then crank the bias pot max CW. What readings do you get? Actually this will be 4 readings, two readings per tube.

I don't think you understood what I asked. Read it again and tell me the 4 voltage readings you get. That's all I want to know at this point.

[pompeiisneaks]

I tried to answer as best I could but the voltage reading of 0mV, 10mV, 200mV, 110mV, 28mV and any other number in between constantly changing is somewhat hard to deliver.  That's what I was trying to explain before.  I can't get a stable reading that I'd call "good".  Maybe I need to go back to it now that I turned the presence down to 0 though.  I'd only consider a reading as 'good' if it stays within 100 mV of its reading for more than 1 second... and even that's stretching it.  I hope that's clear.  There IS no solid, consistent reading, its all over the map.

I'll try again, and see if I can get it to stop moving.  The only way I DID get a solid, consistent reading was with the tubes back in and the presense at 0.  Then things seemed to settle down.  Once I turned it back up, though, it seems fine?  I'm confused.

~Phil

[pompeiisneaks]

OOOOKay... I just figured out why my readings are all over the place.  Its the leads I'm using they're the small clip hook type.  They're not making solid connections, that randomness was noise on them.  If I pulled gently against the hook, suddenly my readings came in good.  /sigh.

So for the tubes L and R

CW 73mV and 65mV
CCW 67mV and 62mV

I could still be getting mediocre readings due to the leads, not sure. but my good leads that came with the fluke are point type only so I'd have to have both hands in the chassis at once and I'm not gonna do that :)

As I had seen above once I got good consistent readings with the tubes in, things were looking pretty good, and I think many of my high readings were due to the leads having no consistent connection I thought I was reading.

~Phil

[pompeiisneaks]

and on that note, I'm off to the local electronics shop to buy some real leads :) 

~Phil

[sluckey]

CW 73mV and 65mV
CCW 67mV and 62mV

PUT THE METER PROBE ON PIN 5! You ain't gonna measure any millivolt stuff. I'm expecting something in the neighborhood of -40 to -50 VOLTS DC.

[pompeiisneaks]

OMG SORRY! lol I didn't even see 'pin 5' I was thinking still of the current

You may need to come over and smack some sense into me ;)

I'll go get that now.

(I can hear you cursing from here).  I did get the - bias voltage at the bias section, but not on pin 5, I'll DO IT :)

~Phil

[pompeiisneaks]

Here you go:

CW: -46.0V, -45.9V
CCW: -54.5V, -54.5V

As stated before, with the tubes in, the pin 1/8 to the 1 ohms was:

CW: 31mV, 26mV at -65.6V bias voltage total.
CCW: 53.7mV, 51.4mV at -62.9V bias voltage total.

Grid and Anode voltages are 455V

Thanks for being patient with me :D
~Phil

[sluckey]

I've forgotten why I asked???     

Anyhow, that's a fine adjustment range. You can find a happy operating point somewhere between max CCW and max CW.

[pompeiisneaks]

Lol, I really do apologize for yet again going down the wrong rabbit hole.  So per my previous question, with the voltages near 450, and the datasheet saying for a 6L6GC I should have 116 mA current for two tubes, that's 58mA for each right?  But since my max seems to be about 53.7mV I can just max it out and I'll be in safe range no?

~Phil

[Willabe]

CW: -46.0V, -45.9V
CCW: -54.5V, -54.5V

As stated before, with the tubes in, the pin 1/8 to the 1 ohms was:

CW: 31mV, 26mV at -65.6V bias voltage total.
CCW: 53.7mV, 51.4mV at -62.9V bias voltage total.

Wait a second, how is he getting a max -54.5dcv full ccw with tubes out and -65.6dcv cw with tubes in?

And even if he has the cw/ccw backwards (which he probably does) where's the extra -11.1dcv's coming from with tubes in?

[Willabe]

Grid and Anode voltages are 455V

You must mean screen grid, right?

[sluckey]

I'm guessing that -65.6 is NOT measured on pin 5. Probably right on the bias diode/first cap. But who knows? Just another red herring. 

[Willabe]

I only like pickled herring in cream sauce. 

[pompeiisneaks]

Grid and Anode voltages are 455V

You must mean screen grid, right?

Yes, pins 4 and 6 have identical voltages, 455. Sorry, the input grid should def not be there :)

~Phil

[pompeiisneaks]

I'm guessing that -65.6 is NOT measured on pin 5. Probably right on the bias diode/first cap. But who knows? Just another red herring. 

Yeah that's why I called it bias voltage 'total' I don't know how you'd call it, but that's at the resistor right by the diode as the bias comes in.   The per tube bias voltages were above:

CW: -46.0V, -45.9V
CCW: -54.5V, -54.5V

~Phil

[HotBluePlates]

Did you use a 10kΩ or 50kΩ trim pot?

If it's a 10kΩ trim pot, do you have any resistors on hand? What values?

[pompeiisneaks]

It's the 50k trim pot.  The standard one that comes with Doug's 5F6A bassman build.

~Phil

[pompeiisneaks]

Here are pics of the finished build (Its all of the build, the last 6 are from today showing off the final project.)

I've got a cabinet on order with 4 speakers from mojotone too.  Once that's all buttoned up, I'll show that too :)

https://goo.gl/photos/5VLYdHztRaMJHN5V8

~Phil