Search found 164 matches
- Sat Feb 27, 2021 10:08 pm
- Forum: Marshall Discussion
- Topic: 100W "Blackflag" presence/bias issue
- Replies: 14
- Views: 3490
Re: 100W "Blackflag" presence/bias issue
I had tried moving the nfb wire, to the pot and to the selector. Chopsticked it in different spots, etc... I didn’t observe any change with the bias. Actually, with low presence settings, the amp goes back to normal. With presence on 0, the bias current goes up. If I disconnect the nfb, the bias is ...
- Thu Feb 25, 2021 8:37 am
- Forum: Marshall Discussion
- Topic: 100W "Blackflag" presence/bias issue
- Replies: 14
- Views: 3490
Re: 100W "Blackflag" presence/bias issue
Nope, Mullard xf2 but put some ruby tubes after I discovered the issue. It still does it after a significant warm up period.
I’m at a loss...
I’m at a loss...
- Wed Feb 24, 2021 8:42 pm
- Forum: Marshall Discussion
- Topic: 100W "Blackflag" presence/bias issue
- Replies: 14
- Views: 3490
Re: 100W "Blackflag" presence/bias issue
Cleaned the board with alcohol, underneath as well. No change...
If it’s an oscillation, where could it be coming from?
If it’s an oscillation, where could it be coming from?
- Mon Feb 22, 2021 11:12 pm
- Forum: Marshall Discussion
- Topic: 100W "Blackflag" presence/bias issue
- Replies: 14
- Views: 3490
Re: 100W "Blackflag" presence/bias issue
I’ve checked all the grounds, replaced the nfb wires so they are far from everything, tried changing all the caps, measured all resistors. No change. I changed the presence pot, same... I grounded the preamp and the issue is still there, so it comes from the power stage. If I lift the nfb resistor, ...
- Tue Jan 26, 2021 9:28 pm
- Forum: Marshall Discussion
- Topic: 100W "Blackflag" presence/bias issue
- Replies: 14
- Views: 3490
Re: 100W "Blackflag" presence/bias issue
All right back to the black flag! I forgot about it... So I changed the Pi caps (all 3 .1uf), no change. I changed the bias caps, no change. Changed the .022uf in the Pi too and the presence cap. As soon as I turn the presence pot, the bias lowers significantly ( around 10ma). I also found out the s...
- Fri Jan 22, 2021 1:43 am
- Forum: Dumble Discussion
- Topic: Tweedle Dee HUM... grrr
- Replies: 13
- Views: 961
Re: Tweedle Dee HUM... grrr
Success!!! I noticed I had grounded the bleeding resistor from the first cap near the power tubes. I removed it and soldered another one across the cap this time. Most grounds looked good but redid them just in case. I also moved the mains ground to the heaters ct. I’m not 100% sure what the issue w...
- Thu Jan 21, 2021 11:46 pm
- Forum: Dumble Discussion
- Topic: Tweedle Dee HUM... grrr
- Replies: 13
- Views: 961
Re: Tweedle Dee HUM... grrr
Measured resistance to ground everywhere and everything is between 0.1 and 0.2 ohms. As I mentioned before, continuity is good everywhere. Checked the inputs, all is good. Most of the hum goes away with V1 but not all. It does with V2 though.
I’ll reflow the joints and report back.
I’ll reflow the joints and report back.
- Thu Jan 21, 2021 11:14 pm
- Forum: Dumble Discussion
- Topic: Tweedle Dee HUM... grrr
- Replies: 13
- Views: 961
Re: Tweedle Dee HUM... grrr
Thanks Phil. I want to confirm something: if the grounding scheme was an issue, I would have had the hum from the start, right? So assuming it’s not a design issue,since the hum is new, I guess it would be a mechanical one and the main culprit in that case would be a bad ground connection? Checked l...
- Thu Jan 21, 2021 10:20 pm
- Forum: Dumble Discussion
- Topic: Tweedle Dee HUM... grrr
- Replies: 13
- Views: 961
Re: Tweedle Dee HUM... grrr
Ok, so I’ve determined it’s a 60hz hum (played on youtube, exact same pitch). If it was a ground loop, wouldn’t it have been present before? The scheme I used is pretty similar to the one in the layout of Charlie Wilson in the files section. I checked the continuity in the power section, everything ...
- Thu Jan 21, 2021 9:53 pm
- Forum: Dumble Discussion
- Topic: Tweedle Dee HUM... grrr
- Replies: 13
- Views: 961
Re: Tweedle Dee HUM... grrr
Thanks! How would I check for rectified hum? Continuity for ground is good everywhere. Chopsticking doesn’t seem to indicate anything. Also, how could I test if it’s the elytics? Just unsolder and measure them? Hum issues are super common but in over a decade of building amps, it’s a first. My build...
- Thu Jan 21, 2021 8:22 pm
- Forum: Dumble Discussion
- Topic: Tweedle Dee HUM... grrr
- Replies: 13
- Views: 961
Tweedle Dee HUM... grrr
So, for no apparent reason, my TD started to hum like crazy. Not a buzz, it’s a low pitched, muffled sounding hum. It’s only present with the volume turned up, on either channels, with or without anything plugged in. I built that amp a few years ago, never had that issue. With V1 removed, the hum is...
- Sun Dec 20, 2020 1:31 am
- Forum: Fender Discussion
- Topic: Tone/Volume: need help to brighten things up
- Replies: 9
- Views: 1473
Re: Tone/Volume: need help to brighten things up
I thought about decreasing the first cap to a lower value, I think I had tried that but it mostly took low end away...
On these types of amps, why does adding a cap across the volume pot doesn’t do anything?
On these types of amps, why does adding a cap across the volume pot doesn’t do anything?
- Sat Dec 19, 2020 8:53 pm
- Forum: Fender Discussion
- Topic: Tone/Volume: need help to brighten things up
- Replies: 9
- Views: 1473
Tone/Volume: need help to brighten things up
Hi, I hope everyone is safe and sound in those strange times we live in. Over the years, I built several tweed and brown combos (5e3s, 6g2, 5d3, tweedledee or even a Marshall 18w). I’m not sure why, but all of them sound dark... the tone knob is always maxed out. I’m more of a plexi player, so me ea...
- Sat Apr 11, 2020 8:18 pm
- Forum: Fender Discussion
- Topic: ‘63 6G3 unpleasant overdrive issue
- Replies: 13
- Views: 3660
Re: ‘63 6G3 unpleasant overdrive issue
NFG, it sounds like our issue was similar. My 6G3 had original its speaker and preamp tubes (1 RCA and 2 TungSol). The amp turned out to be ok for the most part. I upped the filtering a tad and installed grid stoppers on the power tubes to minimize high end oscillation. It helped a bit but not much....
- Sat Apr 11, 2020 7:50 pm
- Forum: Fender Discussion
- Topic: Current 6L6GC ?
- Replies: 7
- Views: 1366
Re: Current 6L6GC ?
+1 for TAD GC or WGC (more mids).
Remember they are rated for 30W pd.
Remember they are rated for 30W pd.