annoying noises

[yunger]

i'm getting a sizzle/crackle/popping sound when quickly changing chords or strumming fast/hard. it's as if the amp doesn't like a signal with multiple frequencies. it get's worse if i use a fuzz pedal. the noise sounds like the crackling and popping you here on old records.
it could be a bad speaker but i sure hope not. it's a new weber alnico 10". i've ordered new power tubes but i doubt that's it. otherwise, the tubes that are in it died awfully quick.
i see terms like oscillation, blocking distortion, crossover distortion on here alot and being as paranoid as i am i wonder if i have those symptoms. i'll attach my schematic in case i made an obvious mistake. any suggestions?

[txstrat]

I'd change the preamp tubes for known good ones first.

[Howlin' Mad Mac]

Interesting build

I've no suggestions as I'm still learning my way around the inside of a tube amp myself tho I'm no stranger to reading a schematic. Took a look at yours & find it quite interesting. Was just wondering if this was something you came up with yourself, something you found posted somewhere online or is it a clone of some kind?

[tubeswell]

i'm getting a sizzle/crackle/popping sound when quickly changing chords or strumming fast/hard. it's as if the amp doesn't like a signal with multiple frequencies. it get's worse if i use a fuzz pedal. the noise sounds like the crackling and popping you here on old records.
it could be a bad speaker but i sure hope not. it's a new weber alnico 10". i've ordered new power tubes but i doubt that's it. otherwise, the tubes that are in it died awfully quick.
any suggestions?

1) When the tubes died was there smoke? (from your PT?)

2) If the pT is still workin', what are your idle voltages for plates, screens, cathodes, and B+?; and

3) What VAC have you got across all your PT secondaries (including your heater winding? - and if you have got VAC on your PT still - assuming its not deadski (which it might be?), are the tubes' heater filaments still glowing at all or have they gone west?

[loudthud]

Curious about some of the resistor values. Why R10=820 and R15=1.2K? Have you tried the more conventional R10=1.5K and R15=470?

[yunger]

sorry, i didn't realise there were so many replies already. i haven't really done anything to the amp yet until i get some potential replacement tubes.

mac, the circuit is arranged based on pretty standard, known configurations to suit my playing needs. i replaced the original pro jr circuit board with this and it sounds way better....to me.

tubeswell, i don't know if the tubes really are bad. i was just saying that they've only been in there for a short period of time and i'd be suprised if they failed so quickly. the tube filaments do appear to heat up normally on visual inspection. strange that the lamp was blown last time i turned on the amp....maybe i should check voltages.

loudthud, r10 is 820 based on my naive understanding that it would spice up my preamp a little. turns out, i think any value there will produce basically the same result since this is a clean preamp. the pi is a cut & paste of a vox pi and gets pretty dirty. i may change that.

[loudthud]

loudthud, r10 is 820 based on my naive understanding that it would spice up my preamp a little. turns out, i think any value there will produce basically the same result since this is a clean preamp. the pi is a cut & paste of a vox pi and gets pretty dirty. i may change that.

In my experience subtle changes like R10 and R15 can sometimes give unexpected results because they interact with things like B+. From your description, I would suspect one or more of the preamp stages are clipping prematurely. But, it certainly could be the speaker. Any way to try the amp with a different speaker or play another amp through the Weber speaker?

[yunger]

i might have found the problem. i get crackling when i wiggle v1 or the wires attached to the socket. same with different tubes in the socket. i guess there is either trash in the socket or needs retensioned(can this even be done on a 9-pin?) or bad solder connection or broken wire.

[Mandopicker]

Might it be a good idea to move C1 and use it to bypass R3 with the positive side toward the tube?

[yunger]

Might it be a good idea to move C1 and use it to bypass R3 with the positive side toward the tube?

c1 is actually a filter cap. as to cathode bypassing, that was just a matter of choice.

this may or may not be relevant but why is the plate voltage so much lower on v1a than v1b? shouldn't they be the same. plate resistors measured correctly.

[RWood]

Are you getting any DC voltage on the grid of the second triode?

I would suspect the coupling caps, especially C1 but would also look into all solder joints around V1.

Can't say about retensioning the socket - try it and see, use the finest pick tool you have.

RWood

[yunger]

i still have crackling problems.
i've replaced all tubes, chop sticked everything multiple times, pounded the amp with my fist, reflowed all solder, checked for shorts, checked all connections. still making the noise.
i wonder if the power transformer is arching internally. it is tiny and it's current rating is half what the circuit draws. it gets physically hot after playing for a short while. i've noticed that the crackling starts after the amp has been on for a while or after playing the the amp cranked. once it starts to crackle it continues to do so at any volume. also, originally i used a 1 to 2 amp main fuse...i decided to put a .5A fuse in there for safer protection. it blew the first time i cranked the amp and played for a few minutes.
is it a reasonable assumption that the pt might be faulty?

[tubeswell]

i wonder if the power transformer is arching internally. it is tiny and it's current rating is half what the circuit draws. it gets physically hot after playing for a short while. i've noticed that the crackling starts after the amp has been on for a while or after playing the the amp cranked. once it starts to crackle it continues to do so at any volume. also, originally i used a 1 to 2 amp main fuse...i decided to put a .5A fuse in there for safer protection. it blew the first time i cranked the amp and played for a few minutes.
is it a reasonable assumption that the pt might be faulty?

If the PT is only rated for half the current draw you are actually getting, I'd say its a fairly good possibility that PT is stressed/buggered. And cracking and popping can be a smokin' PT. Have you watched it while it is cracking with the back off? Is there smoke coming from the PT?

Re: the fuse, what tubes are you running?

[yunger]

If the PT is only rated for half the current draw you are actually getting, I'd say its a fairly good possibility that PT is stressed/buggered. And cracking and popping can be a smokin' PT. Have you watched it while it is cracking with the back off? Is there smoke coming from the PT?

Re: the fuse, what tubes are you running?

i haven't watched it and haven't seen smoke but there is definately a smell. yeah, i'm getting a new PT. it's not worth the risk. plus, the amp sounds like absolute mush at higher volumes.
the tubes are (2x)el84 cathode biased, (2x)12ax7. based on similar amps i chose a T2A primary fuse.

[tubeswell]

The correct way to size the mains fuse is:

multiply volts with amperes (for each winding) and you get VA. Sum up the VA values and you get the whole VA of the secondaries. Divide that by the mains voltage and you get the primary amperage. Take the nearest value and multiply by two.
For instance
PT:
300v - 200ma = 60va
6.3v - 4a = 25.2va
50v - 80ma = 4va
89.2 va altogether

89.2va / 110v = 0.81a

Match to 1A and multiply by two = 2A mains fuse.