![]() First, we are assuming you have some hum from that source, you may well not. This is not a high gain amp.Īs to making a B+ voltage divider for the heaters, several thoughts. If you have not yet taken possession of the amp, perhaps a good listen first before trying to modify the thing for hum/noise we do not yet know exists. If the first two B+ filter caps are good, I doubt a choke will make it any quieter. replacing it with a choke would raise that B+ to closer to the screen voltage. The 10k resistor in the B+ is there to drop the B+ by 40v for the preamp, as well as be part of the decoupling. I am not saying it is a bad idea ultimately, but do it for the right reasons. Just changing the one part because some othe circuit used it in similar position, is not a good reason. 047 elsewhere, but it was also in a different circuit. Remember, the amps are about circuits, not parts. The input cap blocks any DC riding on the input, but mainly serves to limit the low end response, which would suck power and probably overdrive the speaker.įor transformer manufacture codes, you tell us, look on the part. Most of the current to the driver plate comes through the primary of that transformer. Now stepping on the switch switches from high gain to low. But really, who plugs two instruments into one channel?Īn old trick is to plug the guitar into one jack, and then a simple shorting stomp switch into the other jack. yes, if you plug something into both, then each has a 68k in series and the resistors do their best to mix it. And a great deal of the rest of the amp world do as well. Fender has used this arrangement for decades on end. This is a basic 2/1 voltage divider, so using J2 cuts the signal input exactly in half, which is a 6db reduction. In other words, there are now two 68k in series from the input to ground and the tube gets the signal from the middle. ![]() The tube gets the signal from the junction of the two. From J2, the signal flows through the other resistor, but the remaining one is now grounded through J1. If you plug into J1, the two resistors are in parallel for 34k, and the signal flows through it. You already HAVE low and high gain input jacks, that is what the two resistors do. Try gathering your thoughts so it is easier to read. I'm almost 100% there with this amp, just need to fine tune it for maximum clean headroom.Wow, eleven posts in an hour and five minutes. Malcolm, if your burnt out from my endless noise quest dont sweat it! Maybe somebody else can chime in with some suggestions. Maybe upping that again would clean it up? But, remember it had a 1k5 cathode bias resistor, now its 330ohm. I could swear it wasnt as crunchy when I got it but with all the hum it had its hard to be certain. Can I hit the 6AQ5's with all that? Might increase headroom. What about higher voltage? My PT puts out 352v on the screen but I dropped it down to 293v via a limiting resistor. ![]() Any values that can be altered for more clean headroom? I've already got a JBL in there but it starts getting crunchy at 11 o'clock. Now that noise is no longer an issue, I'd like to tweak it a bit for later breakup / more clean headroom. Well I might as well keep my mega-thread going cause now its all fun stuff! Again, I'm not well versed on transformer wiring so this may be out of my reach and over my head.īut if theres a way to check that each wire is were it should be I would like to. Could that be the issue or did the tech who installed it screw something up with the wiring? He's the guy that put the 1meg resistor inline with the pilot lite I presume. The PT has very thin wires, unlike any fender unit I've ever seen. Can I use acetone on a q-tip to clean the tube sockets? I really thought it was the tubes, but tried 4 nos GE 6aq5's and that didnt change things.I've cleaned and re-tensioned the pins.If my pot cleaner is conductive,that would be a bummer. It's a low hum that comes on instantly when the amp is switched on and gradually gets louder for five seconds, kinda the same amount of time it takes the tubes to light up. My hum is not affected by volume/tone adjustments. My amp appears to have lived inside somebodys house all these years, its in quite good condition with no rust anywhere. Thats an interesting link! How on earth would you be able to tell if your wax impregnated board had retained moisture and become conductive?
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