need some help please!

[medicman]

i am new to the forum so let me start by introducing myself my name is wendell and i'm from arkansas i am a bass player but i play other instruments also. i was hoping someone here could help me with a problem i'm having. i have a acoustic g100t amp that quit on me it's dead no heater voltage. the heater voltage is present from the power trans but no tubes are lit. i found two rather large resistors burnt and figured after checking all the 6ls's that one of them was shorted and i think this is what caused the resistors to burn into or at least i hope it is this simple. but my problem is i cant figure the value of them as only one i could make outpart of the bands the other is completely gone. the one is a 1.01meg they are side by side on the circuit board. i'm not good at reading schematics so i took a couple of closeup pics of where they are on the circuit board hoping someone could help me idenify them. i realize that something had to have caused both of them to burn into and i'm hoping it's a tube issue but never the less i still have to replace the two resistors. anyway any help would be greatly appreciated. thanks, wendll.

[tim]

they might be the R5 and R6 filament balancing resistors (100 ohm 1 watt) but not being able to see the bottom of the circuit board, it's hard to say. where do the ends opposite of the ground connection go?

[medicman]

not sure exactly what you mean.what would i look for?

[Euthymia]

My guess is that those were R5 and R6 (and that you made a mistake reading one of them as 1.01M), and that they were taken out by a tube element shorting to a filament.

There's probably also a burnt up PCB trace or other wire between the transformer leads and the tube sockets.

[icefloe01]

My guess is that those were R5 and R6 (and that you made a mistake reading one of them as 1.01M), and that they were taken out by a tube element shorting to a filament.

There's probably also a burnt up PCB trace or other wire between the transformer leads and the tube sockets.

There is a chance he's right on it being a 1M though. On the first page of the schem. where the input jacks are located, there is R3 located nearby C1, a 22uF 50V cap tied directly to V1 with R4 680ohms, and in the middle of the V2 circuit is C4, a 40uF 450V cap immediately followed by R19 and R20 both 1M resistors (though unlikely candidates as there are no assoc. caps). And on the left side of the first pic next to C4 are both a 47K and 470K resistor which would align with R11 and R13. The only thing that throws me is that this where the feedback circuit (red wire) comes back onto the board... So we still need a pic of the other side of the board to really figure it out.

Eric

[tim]

If you're reading a color code as brown black black, that its a 100 ohm resistor. A 1.01 meg resistor would be a 1% resistor and I doubt there are any of those on there

[icefloe01]

If you're reading a color code as brown black black, that its a 100 ohm resistor. A 1.01 meg resistor would be a 1% resistor and I doubt there are any of those on there

Actually, brown black black would be 10ohm brown black brown would be 100ohm. Brown black green would be 1M. Not all 1 Megohm resistors are 1% as I see 5% carbon film all the time where I work.

Eric.

[Enzo]

You can see 5%, 10%, even 20% 1M resistors, but not 1.01M resistors. THOSE would be the 1% he mentioned. And not likely in a guitar amp.

[icefloe01]

You can see 5%, 10%, even 20% 1M resistors, but not 1.01M resistors. THOSE would be the 1% he mentioned. And not likely in a guitar amp.

Good point. And just looking at the digits "101" indicates that the first three color bands he saw could have been brown black brown which of course would the 100 ohm filament resistors. Funny thing is, the parts list at the end of the pdf does not match the schematic!

Eric.

[tim]

you're right and I have egg on my face

10 ohm is brn blk blk. where was my head? I've been doing this for nigh on 40 years and I still screw it up sometimes.

I guess what I was really trying to get across is that if the resistor were a 1.01 meg, it would've had to of been a 1% resistor and I doubt that there is anything in that amp that is so critical as to have to use one of those in there. I have seen amps where a 10% was spec'd out but saw a 5 or even a 1% in there instead, probably because they got a good deal on several reels of the better parts

[Enzo]

I have a bunch of 1% parts, I got them either free or from surplus. They don;t need to be 1% for guitar amps, but they work just fine. I also have some odd values that are close enough to common values. Like 103k resistors. Those tend to be closer to 100k than many of the 100k carbon comps in the drawer. And 95uf caps are close enough to 100uf for me.

We used to know a tech who thought everything was rocket science. He went so far as to buy the same 4558 op amps from each factory, thinking somehow the 4558s that Peavey used were tested for god knows what and were different in some way from the ones that Fender or SLM used. We were always plotting on blowing this fellow's mind with such things as 1480 ohm resistors. Stick one in place of a 1500 ohm cathode resistor and watch the fun as he tried to rationalize why that part value must have been selected.

[icefloe01]

I guess what I was really trying to get across is that if the resistor were a 1.01 meg, it would've had to of been a 1% resistor...

You're right on that and I failed to pay attention to that little detail in your original post. I'll have mine scrambled please. Did you happen notice what I was talking about with the parts list?

Eric.

[tim]

You're right on that and I failed to pay attention to that little detail in your original post. I'll have mine scrambled please. Did you happen notice what I was talking about with the parts list?

Eric.

No, I didn't look at it all that closely, but it wouldn't have been the first time that happened. I have found that HArtke stuff isn't always right, especially after they were bought by Samson. Schematics don't match the part designators, etc which makes for some real interesting troubleshooting. I rarely work on Harke stuff anymore anyway (the new stuff) as it is all surface mount stuff and I just don't have the patience or eyes for that stuff anymore. I don't depend on repairing amps for my livelyhood any longer so I can kind of pick and choose what I work on these days. It's basically a hobby now. I have a friend that owns a music store and he keeps me supplied with stuff to fix.

[medicman]

well let me ask this do you think that i could use two 100 ohm 1 watt resistors in their place and be okay?

[medicman]

picture of one of the resistors

folks this is one of the resistors that was taken out. hope this helps. i dont know if they both are the same or not.