Preamp Tubes? - Who, What, When, Where, Why, and How?

[MM54]

I remember getting high in high school before doing a lab in Chemistry.. Man.. Those Bunsen burners were awesome when you were stoned.. The strikers too..

Those are awesome no matter what state you're in

Especially the strikers

 

[RiverRatt]

Matt, see if this makes sense on that shorts test we were talking about. This info is from the TubeSound B&K 707 blog.
TubeSound » Blog Archive » B&K 700 & 707 tube tester

In the lower “Switch” section, the controls are:

A & B = Filament connections
C = Lockout switch. This switch will lockout (open) one pin, with the pins being standard RTMA numbered (switch position 1 opens pin 1, switch position 2 opens pin 2, etc.). If no pin needs to be locked out, then position 12 is selected. Typical lockouts are (a) control grid has connection to 2 pins, the higher numbered pin gets locked-out; (b) tubes with additional heater tap, such as 35W4; (c) the Shell pin of metal envelope tubes (often pin 1, example 6SA7).
D = Selects the control grid for Emission test and grid leakage test. For diode and rectifier tube sections, ‘D’ selects the Plate pin. Also, Control D is rotated to every position during Shorts testing. Shorts test is automatic at each switch position — there is no need to press the ‘Shorts’ button on the upper panel.

Using our 6L6GC example, I would set the lower panel switches as follows (assuming 6 volt heaters and 63 sensitivity):

A - 2
B - 7
C - 12 (no internal connections to lock out)
D - 5 (for grid leakage and emissions)

The only one I'm not sure about is control D. You said last night that it was probably the plate and that made sense, but the above quote says to select the control grid which IIRC is pin 5 on a 6L6GC? Rotating control D should test (and fail) for shorts between all pins except 2 and 7. Does this sound correct? I don't want to blow up my tester screwing around with the wrong settings.

 

[Cardiac Tom]

Hey all,

Been a long time since I posted here...Hope everyone is well.

Ok, I'm looking to replace my preamp tubes. I use a Marshall JCM900 4100 and I'm not sure if they ever been replaced before...

I play death metal and am very simple...I use no effects other than an EQ in the loop (which I since stopped because of a noise I am getting with it...I know I have an old thread on it somewhere) with a Gibson Explorer...I'm on a budget and I would rather go to a few stores around here to get them...just want to beef up my sound a bit...

Any advice? Overall, I have been happy with my rig, but it is like something is missing...I really don't want to start adding dist. pedals and whatnot unless I really have to. I'm the original owner of the amp (bought it in 91), and I have had power tubes done multiple times (that is due next) but I'm not sure if the preamp tubes have been done. Those I know I can do myself...

I read through some of the threads here and did a search, but it is making my head spin...lol

Thanks in advance!

 

[MM54]

Matt, see if this makes sense on that shorts test we were talking about. This info is from the TubeSound B&K 707 blog.
TubeSound » Blog Archive » B&K 700 & 707 tube tester

In the lower “Switch” section, the controls are:

A & B = Filament connections
C = Lockout switch. This switch will lockout (open) one pin, with the pins being standard RTMA numbered (switch position 1 opens pin 1, switch position 2 opens pin 2, etc.). If no pin needs to be locked out, then position 12 is selected. Typical lockouts are (a) control grid has connection to 2 pins, the higher numbered pin gets locked-out; (b) tubes with additional heater tap, such as 35W4; (c) the Shell pin of metal envelope tubes (often pin 1, example 6SA7).
D = Selects the control grid for Emission test and grid leakage test. For diode and rectifier tube sections, ‘D’ selects the Plate pin. Also, Control D is rotated to every position during Shorts testing. Shorts test is automatic at each switch position — there is no need to press the ‘Shorts’ button on the upper panel.

Using our 6L6GC example, I would set the lower panel switches as follows (assuming 6 volt heaters and 63 sensitivity):

A - 2
B - 7
C - 12 (no internal connections to lock out)
D - 5 (for grid leakage and emissions)

The only one I'm not sure about is control D. You said last night that it was probably the plate and that made sense, but the above quote says to select the control grid which IIRC is pin 5 on a 6L6GC? Rotating control D should test (and fail) for shorts between all pins except 2 and 7. Does this sound correct? I don't want to blow up my tester screwing around with the wrong settings.

Makes sense, and 2-7-12-5 seems like it would be correct. Now that I think of it, D must not be the plate because I had a tube that was testing good for emissions once with a cap, and the cap broke off and it still tested good wtf so I guess the control grid would make sense.

I don't think you'll mess up the tester if you get it wrong, might mess up the tube though, so try it out first on an old one. (wouldn't want 200VDC on your heater, for example )

 

[MartyStrat54]

TOM-The tube I have used most in the 900DR's is a stout Raytheon Black Plate in V1. Some guys claim that V2 affects the tone as well, so I use a Sylvania or RCA in this slot.

If you want current production, then all I can recommend is a couple of Tung-Sol's in V1 and V2.

 

[MartyStrat54]

ALAN-Are you trying to test a 6L6 in the emissions section of the 707?

 

[RiverRatt]

ALAN-Are you trying to test a 6L6 in the emissions section of the 707?

Yes. I'm trying to figure out why it's reading some shorts on all tubes. I want to take a known good tube and see which pins are shorting and maybe track it down.

Any suggestions? I was about to give it a try.

 

[RiverRatt]

The settings work with the 6L6GC in socket 38. I get shorts on pins 3, 4, 5 and 8. I can make the shorts lamp go out by locking out Pin 8 or by pressing the Grid Emission or Test 1 switches.

 

[Cardiac Tom]

TOM-The tube I have used most in the 900DR's is a stout Raytheon Black Plate in V1. Some guys claim that V2 affects the tone as well, so I use a Sylvania or RCA in this slot.

If you want current production, then all I can recommend is a couple of Tung-Sol's in V1 and V2.

Hi Marty...was hoping you'd see this...

What about V3? No matter in this...

For now I just may go with the Tung-Sol's...Others have recommended those as well...

 

[MartyStrat54]

TOM-You can run just about anything in V3, but if you have several tubes try them out to see which one is best to your ears.

 

[MartyStrat54]

ALAN-I had a dinner to attend to and I just got back. I never did that before, so that is something new to me. I don't have any advice to share. However, it does sound like something is awry with your tester.

 

[RiverRatt]

I think the sensitivity adjustment pot was the culprit. I cleaned it good and got the sensitivity set low enough that I'm not getting false shorts anymore. I've got a nice Fluke meter on the way so I can get in there and finish setting the tester up. Hopefully I'll be getting good, consistent numbers soon.

What did I say awhile back about always coming back to the Raytheon black plate in V2? I was playing last night and it was just too fizzy. Put the Ray back in V2 and moved the Mullard back to V1 and it sounded so much better. If I were playing really high-gain stuff and nothing else, I'd probably run two hotter tubes in V1 and V2 but it seems to really limit the amp's versatility.

 

[MartyStrat54]

Yeah when my tester acted up after calibration it was the sensitivity pot. He cleaned it out and it cleared the high reading issue. I hope that you get it up to snuff.

TUBES___Yes ALAN, that Black Plate in V2 just clones itself really well to most V1 tubes and yields a really consistent tone. 8 out of 10 of my customers get a BP. The other two are high gain metal heads and I go with the Electrohome in V2. (Of course the Electrohome makes a sweet V1 in combos, because of the short plates.)

 

[Marshall Mann]

Hey guys!

Matt was right, persistence paid! I won the B&K 700 (super clean, re-ferbed and calibrated) for $163.00!

 

[RiverRatt]

That's not all that much more than I just paid for a multimeter, and it was the cheapest decent one I found.

 

[Marshall Mann]

That's not all that much more than I just paid for a multimeter, and it was the cheapest decent one I found.

Thanks Alan!

What kind of DMM did you end up with? Did you find a Fluke for $150.00???

 

[RiverRatt]

I bought a Fluke 115 for $99 plus shipping. I was looking at an Amprobe 37XR. It would do inductance, too, but the Fluke was a little less and I can't ever remember wishing I could test the inductance of anything. The Fluke has a solid reputation and I think it'll do everything I need.

 

[Marshall Mann]

I bought a Fluke 115 for $99 plus shipping. I was looking at an Amprobe 37XR. It would do inductance, too, but the Fluke was a little less and I can't ever remember wishing I could test the inductance of anything. The Fluke has a solid reputation and I think it'll do everything I need.

Nice score ! You cant go wrong with a Fluke.

Any one I know that does pro electric has one.

 

[RiverRatt]

The Amprobes are nice, too, but I figured if I got one I'd always wonder if the Fluke was better. My old meter is shot. I thought I'd found a dead resistor in the 707 and I just happened to touch the meter where the common lead plugs in and it read OK for awhile, then went back to flashing. No wonder I've been having such a hell of a time calibrating the B&K! I have no idea when it started doing this, but lately I have to rotate the selector a couple of times to get it to come on. This was a good excuse to go ahead and get the Fluke.

 

[MM54]

I'd like to get a nice bench meter some time