[ 'Dead CRATE BV- need help! ]

[Sea Chief]

Amp: Crate Blue Voodoo bv-50 (older type/ head).

Prob: crunchy noises > nr sure prob was Q4 (after great help from thread below) > replaced > but now no sound at all (fuses ok tho).

Schematic: midway down pg.1 #19 CRATE BV amp Ch1 prob- "Crunchy" Noises. - Page 6

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Fwiw, the same 'no sound' started on removal of Q4 for tests. Prior to that just the innitial crunchy noise prob, occasionally ceasing (ie normal low sound) with shorting, or jumpering tests to various X & Y between C19 & MV (V2 area). So we 'narrowed noise down' to here.

So new Q4 in (JFET, J176) we were 95% sure it was this & amp fixed.. so to get the 'dead/ no sound' continuing is a proper kick in the nuts. So I need to re-evaluate.

Any help much appreciated.
S.Chief

[Enzo]

OK, the amp was working all along, the only problem was it had a noise TOO. Now all of a sudden after changing some little part it went silent. it could be a coincidence, but it is almost certainly something you did. IN pulling boards and putting them back, you may have broken a wire off some place or a wire was left unconnected. Or possible a wire is on the wrong push connector.

Accept that the problem exists, just solve it. Don;t try to worry through it in terms of the previous efforts, just pretend you are seeing it for the first time. What would you do? I'd listen, is there ANYthing coming out the speaker? If there is a litle background sound, then parts of it were likely working. If it is DEAD silent, then either the speakers are not connected to the circuit for some reason, or there is no voltage in the circuit. SO look, are all the tube heaters lit? Is there B+ on all the tubes?

[Sea Chief]

Hi Enzo. I thought it MUST be s'thing I did too but Ive troubleshot -all- pg1 possibilities: connectors (check/ 3x), anything broken off (checked/ 3x), spkr connection (check- read 6.8 ohms on its plug b4 inserting/ 2x). All my solder points (check/ each links to adjacent component etc/ none shorting nrby/ all fine b4 too). All these I've crossed off to the nth degree.

All 'fine- but with innitial noise' prior to removing Q4 > tests > 'dead'.

No sound from spkr, not even the quietest of hiss or hum (thats why I worried the OT had gone). All tubes light exactly as before. No ott heat, no smells (I sniffed nr every component!). Just silence. B+ I need reminding of.

[Sea Chief]

Spkr connection ok (check x4). There is usual (just audible) tiny hum for 2mins when Pwr flipped/ ie tube heaters on.. but when Stby flipped/ AmpON, this tiny hum remains exactly same. Defo nothing registering at spkr once ampON.

[g1]

Internal fuses F2 and F3 are ok?
Might as well start with some basic power supply checks. What are the voltages at each end of R99, R74, and R100.

[Sea Chief]

Internal fuses F2 and F3 are ok?
Might as well start with some basic power supply checks. What are the voltages at each end of R99, R74, and R100.

Done: reading schematic L to R..

(R97 side of/ L side of) R99 = 489Vdc
(R74 side of/ R side of) R99= 0v
(R100 side of/ R side of) R74= 0v
(................/R side of) R100= 0v

Big hmmmm..

[Sea Chief]

Internal fuses F2 and F3 are ok?

Yes fuses fine g-one.

I just measured across R99 (150 Ohm 5W)... & read 0/ zero Ohms/ Zilch (yes I did switch MM to Ohmeter). I did look a bit long in the tooth I noticed over the last week or so, somewhat old & darkened, heat-affected looking. But it worked so..

??

[g1]

I think you mean it measures "OL" or something similar? On ohm function with the leads connected you should read zero (short circuit).
With the probes not touching it should read "OL" or something that represents "open" or infinite ohm condition.
I would expect the resistor is open and measuring infinite.
For a resistor to fail to a short or zero ohm condition would be very rare.

[Enzo]

Once, many years ago, I measured a resistor with my ohm meter, and the reading was shorted. I thought to myself that is very odd, I have NEVER seen a shorted resistor. I set it aside and found the next resistor also shorted. Wow, what must have gone on in this piece of equipment? The third shorted resistor made me stop and actually think. How could any of these resistors be shorted, let alone all of them. And I discovered that my meter had a blown fuse, and that particular meter with an open fuse read resistances as zero.

[Sea Chief]

I think you mean it measures "OL" or something similar? On ohm function with the leads connected you should read zero (short circuit).
With the probes not touching it should read "OL" or something that represents "open" or infinite ohm condition.
I would expect the resistor is open and measuring infinite.
For a resistor to fail to a short or zero ohm condition would be very rare.

What I mean is there is no continuity across the resistor. Surely I expect to read 150ohms, theres nothing in parralel to make it read anything else-? and doesnt this tie in exactly with my 0V readings on R74 and R100 side of it?

[g1]

If there is no continuity it is open and needs to be replaced.
Double check there is no low resistance from R99/R74 junction to ground. If so, that could have caused R99 to open and will need to be corrected.
Also check that R74 and R100 are correct resistance.

[Sea Chief]

If there is no continuity it is open and needs to be replaced..

thats what i mean.. so thats a result is it not-? surely that not only accounts for the 0v readings.. but maybe just maybe if it was on its last legs anyway, the cause of the crunchy noise??

Double check there is no low resistance from R99/R74 junction to ground. If so, that could have caused R99 to open and will need to be corrected.
Also check that R74 and R100 are correct resistance.

Done: open-circuit read here. I attatched to both in turn of R74, and R100 (1st checking they link/ did show continuity between) to double-check. No continuity to ground at this junction.

[Ive done these last 2 resistor Ohm readings when amp is off.. your not suggesting need to be done with amp on are you?]

[Sea Chief]

Also check that R74 and R100 are correct resistance.

Yep- both read 10k.

The Q is threfore, is it not, why has R99 150ohm 5w wirewound failed? especially if this is a particularly rare thing, as yourself, & Enzo said so.

[g1]

We were talking about a resistor failing and becoming a short as being a rare occurrence. But it was not 0 ohms, it was OL, open circuit, correct? Zero and OL are as far apart as you can get when it comes to resistance. Be careful to never confuse them.
So it is not uncommon for a resistor to fail in this position, you also said it looked overheated before it failed, so it may have been on the way out already.
As far as the noise, if the resistor had been the cause, it should have still been noisy no matter what we grounded in the preamp, so I doubt it was responsible.

[Sea Chief]

Yes no confusion here at all, I just wrote 0ohms/ zero/ nothing when what I meant to say then was nothing/ a 'I.' on my MM/ an open-circuit (I knew the difference: one is continuity, one there isn't, I knew what I was trying to tell you- basically the resisitor was shot!). Slightly confused about it being 'almost never fail here' but then 'not uncommon for a resistor to fail in this position'.. but nevermind at all. I will replace & report back.

Btw will a generic Maplin (the common UK component 'leccy store' High Street place) 5w wirewound be ok.. or do you suggest a Ohmite/ s'thing specifically GTR tube-amp? and would a 7w 150hm be a better idea in lieu of the failure? a bit bigger but no prob really.