First Build Problems- KLD kit Build

[sluckey]

Shooter,

I didn’t use that little meter to measure the current readings above, I used my fluke and got actual current readings. I do as I’m told boss!!

The readings you posted above are voltage readings. Not what the boss requested.

[2deaf]

Amptata T5 Vacuum Tube Tester EL34 KT88 5881 6L6 6550 Amplifier Bias Current

If it works, I would like to know the current readings for each tube when they are in the V4 socket and then in the V5 socket.

[imgumby001]

Pin 8 to ground is .6mA on v4 & .5mA on v5.

First set-

Tube 1 - V4

1. .6mA
2. 10.6vac
3. 387vdc
4. 365.1vdc
5. -37.1vdc
6. 0
7. 3.7vac
8. .65mA

Tube2 V5

1. .5mA
2. 10.5vac
3. 376.3vdc
4. 358vdc
5. -36.5vdc
6. 0
7. 3.5vac
8. .5mA

Letting the tubes cool then swapping. Readings to follow.

[jammied]

Is that with the bias meter?

[imgumby001]

No, these are pin voltages. I thought that’s what you asked for. I’ll cool her and slap the bias meter in...

[jammied]

That's fine. Continue listening to the pro's. They will be more help


I Was trying to figure why the pin 1&8 voltages were .65 and .5 instead of 65.00mv and 50.00 mv


I suspect v4 is the red plating tube?

[imgumby001]

V4-34mA
V5-48mA

Those are take with the little meter.

[imgumby001]

Those probably are the correct readings, but my little analog meter is hard for me to read. I have no formal electronics training(as if everyone couldn’t tell), so I may read/say a bunch of nonsensical stuff. But, I’m trying as hard as I can to do as I’m told, and listen.

[jammied]

What happens when you swap the tubes

[imgumby001]

After swap-

V4-48mA
V5-33mA

Values are approximated due to the way the meter is numbered. I think it’s pretty close though.

[jammied]

So the red plating follows the tube? What does the one that red plates read?

[imgumby001]

It’s the one running the higher voltage, and yes, the plating follows the tube. But, the other tube is clearly getting high current. You can clearly see the blue excited electrons when the lights are dim in both tubes. Don’t get me wrong, I’m ordering a different set on payday, but I’m weary to to run them only to burn one up potentially. That being said it may be the only way to make a definitive determination. The jj red plates also though. Idk, aside from this red plating issue the amp is finally a playable thing. I’ll be super sad if I can’t get it under control.

[shooter]

If the VDC and current are correct;


I get ~~~~~13.2W on the lower current tube

[jammied]

Yeah not even running 50%.




I would get rid of that pentode/triode switch.


Tone and functionally before dufangly thingy's

[imgumby001]

Oh no, that switch is already gone! It was the number one thing that has so far saved this build!

If the VDC and current are
correct;

I get ~~~~~13.2W on the lower current tube

So, I should have double that?

[imgumby001]

I’m not sure how my question ended up inside the quote...

[jammied]

Pin 8 to ground is .6mA on v4 & .5mA on v5.

First set-

Tube 1 - V4

1. .6mA
2. 10.6vac
3. 387vdc
4. 365.1vdc
5. -37.1vdc
6. 0
7. 3.7vac
8. .65mA

Tube2 V5

1. .5mA
2. 10.5vac
3. 376.3vdc
4. 358vdc
5. -36.5vdc
6. 0
7. 3.5vac
8. .5mA

Letting the tubes cool then swapping. Readings to follow.

With these numbers I can see why it would be red plating.


But with your bias probe the current seems fine. Actually a little low and shouldn't be red plating.




If you go to robrobinettes site there is a bias calculator

[jammied]

Also ... what are the markings on the tubes? As far as 6l6gc, or what not

[shooter]

so we can "assume" for now 1 tube is bad, the one with higher current and red-plating, mark it and leave it out.


with BOTH tubes out;
measure VDC at PIN 5 V4, tube side to ground.  should be steady.  repeat for V5
IF so;
keep measuring and "bang" the chassis a couple times and make sure it's steady


IF so;
measure at the same place and adjust the bias pot 1st max ccw, record VDC.  then max cw, record VDC


post those values
leave the pot at the MAX negative VDC

[imgumby001]

Also ... what are the markings on the tubes? As far as 6l6gc, or what not

The NOS tubes are unmarked- but were purchased as 6L6GC’s.

so we can "assume" for now 1 tube is bad, the one with higher current and red-plating, mark it and leave it out.


with BOTH tubes out;
measure VDC at PIN 5 V4, tube side to ground.  should be steady.  repeat for V5
IF so;
keep measuring and "bang" the chassis a couple times and make sure it's steady


IF so;
measure at the same place and adjust the bias pot 1st max ccw, record VDC.  then max cw, record VDC


post those values
leave the pot at the MAX negative VDC

I get -44.2vdc to -28.1vdc on both sockets. Leaving at -44.2 as per my instructions.

[shooter]

the 3 colors are the "other" paths for problems


NO POWER, wait ~15min
insert a tube into a socket
now;

ohm each path end to end
leave your meter at each end, then wiggle poke prod the physical circuit, so pin 3 to OT "top" you'd verify zero-ish ohms, then wiggle tube, meter dance?, wiggle wire at pin 3, meter wiggle?


ASSUME there is voltage, so wooden stick, face not to close   

[imgumby001]

the 3 colors are the "other" paths for problems


NO POWER, wait ~15min
insert a tube into a socket
now;

ohm each path end to end
leave your meter at each end, then wiggle poke prod the physical circuit, so pin 3 to OT "top" you'd verify zero-ish ohms, then wiggle tube, meter dance?, wiggle wire at pin 3, meter wiggle?


ASSUME there is voltage, so wooden stick, face not to close   

I’m not sure I’m doing this right. There are no readings on most of these points, save continuity on the grounds. I removed the switch, so that point is moved, but I’m not getting any movement from my meter, or real readings of any kind. What am I missing?

[shooter]

pin 4 to the junction of C14/R31 should be about 1k
pin 3 to OT should be 0, but you might have to sharpin your probe tip to "pierce" the OT wire real close to where it comes out of OT


pin 1 to 8 should be 0
pin 1 OR 8 should be 1ohm to ground


do the pin tube-side, then install a tube, bottom side to...........other end, then wiggle tube


you're looking for mis-wire, bad solder, broke trace if it's PCB, anything that could cause a current imbalance besides a bad tube

[imgumby001]

Yes sir!! Copy-copy!!

[shooter]

I was enlisted, AND new my Father 

[jammied]

 




The Russian 6p3s-e always has some blue glow inside the plates. As well as some sovtek 6l6wbg and the relabeled sovtek and russian military tubes. And is normal for THOSE tubes. They also are 25 watt tubes not 30 watt. So red plating is bad but blue inside the plates is normal.




If they are the regular 6p3s and not the 6p3s-e they are rated for max plate voltage around 400 volts or so but still 23-25 watt tubes




Edit:


Robrobinettes bias calculator is showing the 6p3s as a 20watt tube and the 6p3s-e as a 20.5 watt tube.


So with about 400 volts on the plates 35mv or so across the the 100ohm cathode resistors would be plenty hot!

[shooter]

agree, I always consider 6L6 a 20W tube
the 35mV is across the 1 ohm, not 100ohm though

[jammied]

Do you mean because a 6l6gc is a 30 watts max tube and at 70% is 21 watts?


If his nos russian tubes are the 6p3s or 6p3s-e variety then they are 20 watts max and 14 watts at 70%


So my thinking is if he bought them nos advertised as Soviet tubes they are probably 20 watt max.


Not matched very close. What supplier was that?

[shooter]

I did 1 pSE 6L6(EH) build, typically I run 90-100% but they sounded best at about 70% 
I bought same tubes for a repair, they sounded best and behaved well at 55-60% (according to old notes)


"generalities" are a good start, but at the end of day, the amps are basically an individually "tuned" thing

[jammied]

Hmmmm......


From what I have seen on the internet.  There are at least 2 different 6p3s-e tubes and a 6p3s standard that is closer to a 6l6g than a 6l6gc. But most resellers are claiming 6l6gc equivalent even though some are not.


And all of them have different specs. The later ones being relabeled by numerous manufacturers. And supposedly upgraded?


Depending on the particular ones gumby has. They could be running way over max.


The bias calculator is showing either variety of 6p3s as a max of 20 watts. More of a super 6v6




Interesting!

[imgumby001]

I was enlisted, AND new my Father 

No offense bubba, just force of habit.

The Russian 6p3s-e always has some blue glow inside the plates. As well as some sovtek 6l6wbg and the relabeled sovtek and russian military tubes. And is normal for THOSE tubes. They also are 25 watt tubes not 30 watt. So red plating is bad but blue inside the plates is normal.




If they are the regular 6p3s and not the 6p3s-e they are rated for max plate voltage around 400 volts or so but still 23-25 watt tubes




Edit:


Robrobinettes bias calculator is showing the 6p3s as a 20watt tube and the 6p3s-e as a 20.5 watt tube.


So with about 400 volts on the plates 35mv or so across the the 100ohm cathode resistors would be plenty hot!

You’re absolutely right!! I’m sorry I didn’t look at this closer/sooner. Here’s the add;

 For sale are NOS new matched duet of 6L6GC vacuum tubes $13.99/pair.  A representative picture is shown.

They are made by the Famous Russian Reflector factory, 6n3c's designed for up to 50 watts/pair of 6L6s.

Very nice warm sound.

_____

former feedback about these

"just put tubes in my 1973 pro reverb ive had since 1976 ,very pleased good sound"

 

[imgumby001]

Just FYI- the only tube actually labeld 6L6GC is an actual old labeld Sovtek, and its red plating as well. The other unbranded tube is labeled 6L6. The NOS tubs from the add aren’t labeled at all. Clearly I didn’t know what I was looking at when I bought them, thinking they were actual 6L6’s.

[imgumby001]

Luckily, and at the very least, I was smart enough to order some NOS Sylvania’s last night! I did also order another to match the Russian tube that seems to be working ok.

[jammied]

I would put both nos tubes in. Then the one that is reading high with the bias meter adjust bias to 35-37 if possible. Taking note of the plate voltage also.




Then see if it still red plates. I'm betting they are the 20 watt max tubes. So 70% would be 14watts.


Could be to late

[imgumby001]

I’m thinking it’s too late for the one, but I have another on the way, form a different seller. I think it’s obvious to everyone they weren’t an actual matched set, but what can I expect at that price. Just one more lesson learned on this deal. We’ll consider it a small price to pay...

[jammied]

Hopefully you ordered from a different supplier! Some mismatch isn't bad. But that is alot.


They apparently didn't burn the tubes in before matching.


The red plating tube is probably still good. The Soviet tubes are pretty robust but severely misrepresented .

[jammied]

The sylvania's will probably need r55 raised to get full bias range

[shooter]

lets make sure there's music and no glows before raising anything

[imgumby001]

lets make sure there's music and no glows before raising anything

Copy that!!!

The sylvania's will probably need r55 raised to get full bias range

So, what value do you think will do it? Or, would it make sense, albeit a harder part to source, would changing the bias pot to a unit with a broader range be a better overall fix/upgrade? I’d still like to be able to run some EL’s if I get my hands on some.

[jammied]

I wouldn't change anything yet. Just from what I have seen I would speculate that will be the case though.


The power transformer is only rated at 3 amps on the 6.3 volt taps.  I would have to double check but I think el34's will draw about 1.8 amps per tube. Compared to 6l6 varieties that draw 1 amp.

[imgumby001]

If it were 1.5a of draw that would do it, right? I swear I saw mullard el34’s draw 1.5a heater current.

[jammied]

Correct el34's draw 1.5 amps. 12ax7's draw 300ma per tube. 3+.9=3.9 Amps .


I put some el34's in the jtm25 last night. And it uses 4 12ax7's so 4.2 amps total heater current. Then measured the voltage across the heater on the el34's and 12ax7's and still had 6.3v on the el34'S and 6.5v on the 12ax7's


The power transformer didn't seem to be running any warmer than usual after 20 minutes so maybe the el34's would be ok.


Maybe later I will pull the tubes and measure then it will be more clear on the extra load of the el34's.

[imgumby001]

Thanks bubba!!! I didn’t pull the trigger on any 34’s yet, so I’ll wait for your final numbers to come in on that before I make the ultimate call. Im still considering trying to source a bias pot with a broader range and seeing if that doesn’t create a sweet spot for easy bias adjustments for a greater number of tubes, I.e. the 6l6 variety, both american/British and Russian variants, and EL’s. Doesn’t seem like a bad idea at this point.

[imgumby001]

So here’s my latest findings. Received a new NOS 6P3S. It’s matches the cooler running one that has NOT been red plating in the amp. Warmed it up good in v4 position after removing the red plater from that socket. Took it inside and hooked it to the 30w 12” EH that I’ve got in a sealed cab. Leaned into her slowly and she sounded pretty good. Keep in mind I’ve got the bias voltage turned as low as the pot will adjust. Cranked the gain and volume and the amp came to life for the first time! Sounded sweet!! Great bottomy tone, that was rich, if not a bit weak in the treble side. Still, thick and rich. Just when I was starting to feel safe, red plate on the v4 tube! So, not wanting to just chalk it up to bad tubes I swapped positions between the power tubes, and what did I find? The red plate stayed with the socket! Now it never did that before. That specific tube had not fully red plated when the other one was in, so this is the first time I’ve seen it go hot. At this point v4 is my major issue. Short story long, it seems like I’m moving toward either;

1. Getting an actual matched set of 6l6gc’s

Or

2. Changing a resistor to restrict the voltage going to the power tubes.

Does this sound about right to everyone?

[2deaf]

swap tubes, does it follow tube?

the red Plating stays at the socket

[jammied]

Maybe tighten the tube socket pin contacts. Also wouldn't hurt to pull the board and have a peak to be sure that when wiring something didn't get grounded or shorted.

[jammied]

I ordered a set of the "matched" 6p3s tubes out of curiosity.  Hopefully be here tomorrow.


Damn curiosity!!

[sluckey]

You're up against the wall with the bias adjustment, yet you are still red plating. Time to actually do something.

-45.9vdc to -29vdc.

That bias voltage range is more suitable for EL34s. 6L6s would be happier if that voltage range was shifted upward to about -55v to -40v. You can do this by decreasing R55 and/or increasing R51. Simply swapping R55 and R51 just might get it.

[imgumby001]

Maybe tighten the tube socket pin contacts. Also wouldn't hurt to pull the board and have a peak to be sure that when wiring something didn't get grounded or shorted.

I actually wired it out of the chassis. Not that it would be a bad idea to look at it.

You're up against the wall with the bias adjustment, yet you are still red plating. Time to actually do something.

-45.9vdc to -29vdc.

That bias voltage range is more suitable for EL34s. 6L6s would be happier if that voltage range was shifted upward to about -55v to -40v. You can do this by decreasing R55 and/or increasing R51. Simply swapping R55 and R51 just might get it.

It would be ridiculous to argue with that!! Looks like tomorrow I’m gonna be swapping resistors.

[jammied]

V4-34mA
V5-48mA

Those are take with the little meter.

Ok I'm trying to learn something here so dont get me wrong .


If the bias meter used here is reading correctly.   Shouldn't these numbers be within range for 6l6 tubes?