Peavey grid resistor specs. ?

[kmcguitars]

I just got a Peavey Classic VTX 2x12 combo. One of the grid resistors
is blown :smack: The main problem is I can't read the values on these's
resistors? I'm assuming they where changed before? Cuz' I believe
they are Military resistors? They are Black w/t a silver ban and 2 #s
2873 8138 ?? the other is burned. No chance finding a schematic
for free. Anybody have a clue?

 

[Jeff Seal]

Re: Peavey grid resistor specs. ?

47k.....according to the schematic I have.

Jeff Seal

 

[kmcguitars]

Re: Peavey grid resistor specs. ?

WOW! Thanks Jeff That was fast!

 

[lastwinj]

Re: Peavey grid resistor specs. ?

I just got a Peavey Classic VTX 2x12 combo. One of the grid resistors
is blown :smack: The main problem is I can't read the values on these's
resistors? I'm assuming they where changed before? Cuz' I believe
they are Military resistors? They are Black w/t a silver ban and 2 #s
2873 8138 ?? the other is burned. No chance finding a schematic
for free. Anybody have a clue?

with those numbers, it seems to me, that is a 287K resistor made in the 38th week of 1981.

but, it might not be a grid resistor that you found burnt. good luck!!

germ

 

[kmcguitars]

Re: Peavey grid resistor specs. ?

with those numbers, it seems to me, that is a 287K resistor made in the 38th week of 1981.

but, it might not be a grid resistor that you found burnt. good luck!!

germ

It's going across the base of the tube socket ? When the amp is turned
on that tube become CHERRY RED !! What else might it be?
1981 is consistant w/t the timeline of this amp, But it's odd that
ever other resistor in the amp is your STD. color coded ban type.
But the 2 going across the tube base are not? Did peavey use this
style? or are they replacements? ( This is getting confusing :laugh2: )
Maybe I should buy a new multi-meter and meter the good one out?
If that one hasn't drifted off value to far? I'll have a Idea what the hell
it is.

 

[Kent S.]

Re: Peavey grid resistor specs. ?

It's going across the base of the tube socket ? When the amp is turned
on that tube become CHERRY RED !! What else might it be?

That sounds like that tube is drawing WAY to much current, check the bias to it, it sounds like the bias it's receiving is to high (not a low enough negative voltage ... ). You could have a problem along your bias line, not sure how the screen grid is done on that, heck the tube itself could be going bad. I'm going to defer to Jeff and Germ on this one, anything else you guys can think of? If you swap the two tubes, well two from the same pair does it do it in that socket, does the same tube do it in a different position. I wouldn't leave the amp running that long like that. Jeff, Germ?

Maybe I should buy a new multi-meter and meter the good one out?
If that one hasn't drifted off value to far? I'll have a Idea what the hell
it is.

That might not be a bad idea, even if it's drifted a bit you can still match it to a standardized value. ... That tube look indictates another problem for sure though.

 

[kmcguitars]

Re: Peavey grid resistor specs. ?

Thanks Kent! it's the 2nd tube I tried in that socket ! So I'm sure it's
that socket/or related to it. I shut the amp down right away. I'm down
to my last set of unburnt 6L6s. I'm not putting them anywhere near
this amp until this is resolved. This amp was a freebie,So if the problem
is deeper than a resistor or something simple? (The trashman gets some
more work !!)

 

[lastwinj]

Re: Peavey grid resistor specs. ?

Thanks Kent! it's the 2nd tube I tried in that socket ! So I'm sure it's
that socket/or related to it. I shut the amp down right away. I'm down
to my last set of unburnt 6L6s. I'm not putting them anywhere near
this amp until this is resolved. This amp was a freebie,So if the problem
is deeper than a resistor or something simple? (The trashman gets some
more work !!)

if you can get me a pic of the innards i would be most appreciative. it will help me out. be sure to indicate, if i cant saee it, where the key is on the tube socket.

also, now that i know what it is doin, i think it is a screen resistor (not a grid resistor) that went south on you. change both of them, with whatever the schem shows. probably a 470 ohm 2 watter. somethgin like that.

germ

 

[Jeff Seal]

Re: Peavey grid resistor specs. ?

Germ, this one's all yours!!!.... This one must be an early one...... VTX series runs the 6L6's neither fixed or cathode biased, but instead use transistor pre-drivers for both the bias and audio feeds. Grids (pin 5) are tied together through 1.5k resistors and run to a fixed + 15v supply. (no audio). Plates are standard push/pull wired to either side of the OT. Screen grid's are wired to a tap in the OT between the CT and the plate, thus running at lower voltage. Suppresor grid and cathodes are tied, so basically whereas the older Fender Vibrato circuits modulated bias for volume shifts, this design modulates the entire cathode feed for the signal.......weird stuff...huh?

kmc, if you know which pins the resistor in question are attached to, it would help tremendously.....by the way I now doubt they're 47k's....
These are the few amps that defy "common" circuit design.... Do you know if it has the 6465 Pre-drivers? (located at the top left corner of the PCB or corner closest to AC cord) If it has these, they are still available....But the T0-220 package transistors aren't.....all in all you're only hope is just to check every component for well within tolerance........or chunk it in the dumpster and grab a beer!

good luck!...hopefully germ can help you more!

Jeff Seal

 

[Quencho092]

Re: Peavey grid resistor specs. ?

hmmm this is a VTX ? Does the chip read " '75 Classic ". If it does i may have the same exact amp.

 

[kmcguitars]

Re: Peavey grid resistor specs. ?

O.K. here's some pics. Thanks guys for all the input Jeff, At a quick
glance I didn't see a 6465 chip? ( But I'm gonna get a better look in
the daylight) It's a Peavey Classic VTX series. That's all it says and
I believe its 65 watts.The resistor in ? runs from pins 3 to 7. Thanks again Hope the pics help.
BTW, If you look next to the filter cap there's a 1 amp fuse missing.
It poped the 1st time I fired it up. I took the one from my Princeton
to get it working again. (It's now back in the princeton) Ah, yes good
ole' Point to point wiring in that baby !! I hate this PCB IC chip crap :laugh2:
Makes a Cold beer and the trashman look that much better! :laugh2:

 

[Jeff Seal]

Re: Peavey grid resistor specs. ?

Pics helped.... The transistors mounted on that corner (again closest to AC cord) are the discontinued TO-220's... If they're bad, it's almost next to impossible to find them.

The componenets mounted to the tube sockets aren't resistors at all, they are "spike suppression" diodes, (thus why they're black and have a silver band denoting cathode) cut them out and do not replace them. (the slight benefit they provide is greatly outwieghed by the fact they will fail even under normal power-up conditions) The only current production amps that still use them besides Peavey is Crate and Ampeg and it's well known they wish they wouldn't have! No other amps use them...so I can guarantee you they're not that important.... If anyone would like to disagree, that's fine and I'll find you a suitable replacement diode for it..... this explains the weird numbers as the factory designation is 2873.

Jeff Seal

 

[kmcguitars]

Re: Peavey grid resistor specs. ?

Thanks Jeff So my true grid resistors are the ceramic pairs mounted
on the PCB ? I just checked, I don't see a TO-220 chip? Is it on the main
PCB or the power supply board? Maybe it was changed to a different
spec.? I think Someone was inside this amp before ? If the 220 is not
avilable is there a subsititute? This is all weird to me :smack: I'm used
to the insides of BF/SF Fender amps. I may be getting in over my head
with this thing? And to make matters worse no luck finding a schmatic
for this thing?? I found one for a Duece and Mace ( I wish it was one
of them ) You where right on them the grid resistor is 47k. But this
is most likely a whole different beast. May be time for that Beer :laugh2:

 

[Jeff Seal]

Re: Peavey grid resistor specs. ?

My bad, for not explaining...... TO-220 is a description of a transistor, not a part number and not a chip at all! (where did that come from?). The two transistors next to the ceramic resistors attached to the metal "plates" are the transistors I was referring to. Because they have the three legs on one side and the metal "tab on the other.... this is a TO-220 transistor, most of the VTX's had the TO-3 transistors, which look entirely different (round "can" looking transistor's)....

Your actual grid resistors are the 1.5k (brown, green, red and either gold or silver), but a better idea would be to turn the amp on without the 6L6's and check pin 5 for about 15v....

JS

 

[Kent S.]

Re: Peavey grid resistor specs. ?

Germ, this one's all yours!!!.... This one must be an early one...... VTX series runs the 6L6's neither fixed or cathode biased, but instead use transistor pre-drivers for both the bias and audio feeds. Grids (pin 5) are tied together through 1.5k resistors and run to a fixed + 15v supply. (no audio). Plates are standard push/pull wired to either side of the OT. Screen grid's are wired to a tap in the OT between the CT and the plate, thus running at lower voltage. Suppresor grid and cathodes are tied, so basically whereas the older Fender Vibrato circuits modulated bias for volume shifts, this design modulates the entire cathode feed for the signal.......weird stuff...huh?

Ya got that right, BTW I love the original Fender Tremolo ... what did they call it ... Harmonic Tremolo I think, it's the simplest of there designs and it sounds better than the LED/LDR designs ... cool.

kmc, if you know which pins the resistor in question are attached to, it would help tremendously.....by the way I now doubt they're 47k's....
These are the few amps that defy "common" circuit design.... Do you know if it has the 6465 Pre-drivers? (located at the top left corner of the PCB or corner closest to AC cord) If it has these, they are still available....But the T0-220 package transistors aren't.....all in all you're only hope is just to check every component for well within tolerance........or chunk it in the dumpster and grab a beer!

good luck!...hopefully germ can help you more!

Jeff Seal

One place you might look ... www.chipdocs.com as that site will find places that still have obsolete parts stored, and prices. You punch in the part number, they cover lot's of semi-conductors and chip based passives.

 

[Kent S.]

Re: Peavey grid resistor specs. ?

Also, is it just me, or does that top transistor look a bit burnt (brown discolouration) and the deformed look of the PCB at the leads? Try the chip docs site, as you may at least find the original manufacturer and maybe get a spec sheet ... although the site will probably show a replacement for the obsoletes, if you replace them, I'd replace them in a pair (why not? you want the other to go also...). Hope it helps.

 

[kmcguitars]

Re: Peavey grid resistor specs. ?

My bad, for not explaining...... TO-220 is a description of a transistor, not a part number and not a chip at all! (where did that come from?). The two transistors next to the ceramic resistors attached to the metal "plates" are the transistors I was referring to. Because they have the three legs on one side and the metal "tab on the other.... this is a TO-220 transistor, most of the VTX's had the TO-3 transistors, which look entirely different (round "can" looking transistor's)....

Your actual grid resistors are the 1.5k (brown, green, red and either gold or silver), but a better idea would be to turn the amp on without the 6L6's and check pin 5 for about 15v....

JS

AH HA !! I think I see the problem!! The 3 leged tranny on the metal plate
has a broken leg !! Looks like someone droped a bead of solder on it.
It's the one on the right? (Are they cris crossed? ) I couldn't read the #
on it ( it's 3:30 my eyes are bugg'in) Is this the part that can't be found?
Thanks again YOUR A AMP GURU IN MY BOOK !! :approve: :bigthumb:
GOOD EYES KENT !! Just saw your post you nailed it !!

 

[Kent S.]

Re: Peavey grid resistor specs. ?

Is this the part that can't be found?

Obsolete, maybe still available ... Marked in Red, although you can't read it clearly. Check Chip Docs.

 

[kmcguitars]

Re: Peavey grid resistor specs. ?

Thanks Again Jeff and Kent !! The chip part # is 5884. Now if I understand
this correctly TO-220 is the case style? 3 lug w/t a hole to bolt to
the heat sink. The T-03 5884 is round case and can not be bolted
So it can't be used??? Thanks for the link Kent, I'm still waiting for
a responce. I searched the internet high and low for a 5884 in a
TO-220 case....NOBODY HAS EM' I whent to mouser's site ,they
have part #610-2N5884 But my browser kept frezing when I tried
to go to the spec. sheet. But it's safe to assume it's not the 220
case.( that would be to easy) hopefully chip Dr. come's up with
a sub. If not anybody need a pair of Scorpion speakers ? :laugh2:

 

[Kent S.]

Re: Peavey grid resistor specs. ?

Thanks Again Jeff and Kent !! The chip part # is 5884. Now if I understand
this correctly TO-220 is the case style? 3 lug w/t a hole to bolt to
the heat sink. The T-03 5884 is round case and can not be bolted
So it can't be used??? Thanks for the link Kent, I'm still waiting for
a responce. I searched the internet high and low for a 5884 in a
TO-220 case....NOBODY HAS EM' I whent to mouser's site ,they
have part #610-2N5884 But my browser kept frezing when I tried
to go to the spec. sheet. But it's safe to assume it's not the 220
case.( that would be to easy) hopefully chip Dr. come's up with
a sub. If not anybody need a pair of Scorpion speakers ? :laugh2:

Find (from Chip Docs) the original manufacturer of the part, go th their site, and plop in the number, they should present you with a suitable relplacement ... On some TO-220 cases the part that contacted the metal was a used as a heatsink, and nothing more ... hence the heat sink that it is attached to ...However I can't say that for all, but it's a good bet that that is all it is, even if used as a ground plane reference ... Again I can't say for sure ... but odd are ...