Fender - (preamp hiss/cured) Now have buzz/sputter

[Janglin_Jack]

I changed the only carbon comp in in the amp which was the 3.3M reverb mix resistor.

Can anyone help me understand why three JAN Phillips 12AT7 would cause this buzz but a JAN Phillips 12AU7 would cure it?

Is it the gain, or some other consideration?

[Janglin_Jack]

Wow. As noted previously, I changed the 3.3M resistor from the reverb driver from Carbon Comp to Metal Oxide. Popped in a 12AT7 as before and played it loud. No hint of noise.

I guess it was a bad resistor. Sure took me a long time to get to it. Amp is sounding really good. Even though I wasted a lot of time, I found it and I think the amp is better for all the extra work.

Mike

[Lefty Lou]

Wow. As noted previously, I changed the 3.3M resistor from the reverb driver from Carbon Comp to Metal Oxide. Popped in a 12AT7 as before and played it loud. No hint of noise.

I guess it was a bad resistor. Sure took me a long time to get to it. Amp is sounding really good. Even though I wasted a lot of time, I found it and I think the amp is better for all the extra work.

Mike

Hey Jack, I'm glad you got it figured out. The carbon comp resistor is what I would have examined for "noise" content although a carbon film resistor would do just as well as a replacement. When you mentioned, where there any differences between the JAN Philips ECG 12AT7 and the JAN Philips ECG 12AU7, I concluded it's just a case of having a slightly noisy JAN Philips ECG 12AT7's combined with a noisy carbon comp resistor which exacerbated your noise levels at higher volumes.

I've had more than a few JAN's and NOS Philips ECG 12AT7s, and just because the tubes are silk screened "JAN" doesn't mean a lot to me since I've had some questionable operation from them in amp circuits.

[Janglin_Jack]

Hey Jack, I'm glad you got it figured out. The carbon comp resistor is what I would have examined for "noise" content although a carbon film resistor would do just as well as a replacement.

I would have expected "hiss" from this resistor. When I got that buzz riding over the note, I thought of everything but a resistor. The buzz at high volume had me scratching my head, thinking anything from crossover distortion to blocking distortion. I didn't have a 3.3M at the time I was building this and have a box of old carbon comps, (forget where I got them). I happened to have that value and popped it in. Turned out to be a mistake.

Would have saved me some time if I didn't use it in the first place, but this was a good learning excercise. Got to use my new scope and learned a few things along the way with this build.

Taking to practice Thursday so I can play it loud for 4 hours. We'll see how it performs.

Mike

[Lefty Lou]

Hey Jack, I'm glad you got it figured out. The carbon comp resistor is what I would have examined for "noise" content although a carbon film resistor would do just as well as a replacement.

I would have expected "hiss" from this resistor. When I got that buzz riding over the note, I thought of everything but a resistor. The buzz at high volume had me scratching my head, thinking anything from crossover distortion to blocking distortion. I didn't have a 3.3M at the time I was building this and have a box of old carbon comps, (forget where I got them). I happened to have that value and popped it in. Turned out to be a mistake.

Would have saved me some time if I didn't use it in the first place, but this was a good learning excercise. Got to use my new scope and learned a few things along the way with this build.

Taking to practice Thursday so I can play it loud for 4 hours. We'll see how it performs.

Mike

After you work with your scope more and become more accustomed to using it, things like a noisy component can be narrowed down quicker and addressed. I'd like to hear how your amp performs at rehearsal this Thursday. I played through my friend Chris' Fender SFSR amp w/KT66's last night. Another friend Jerry, brought his lefty Fender Japan 62' Strat w/Texas Special Pickups and .047uF BB tone cap. Chris has a old "beat" Ibanez TS-10 that I played through at Gain 8, Tone 7, and Volume 5, with the amp Volume 2, Treble 7, Middle 7, and Bass 5. I got some absolutely stellar tones that were clean, articulate, powerful, rich, and full with harmonic overtones. The TS-10 delivered just the right amount of distortion edge, and here I had just been thinking of getting rid of my TS clones like my Keeley Voodoo Labs Sparkle Drive and Fulltone Full-Drive 2 Mosfet pedals because I was getting tired of that sound. It just goes to show that our perceptions can be misplaced until presented in the proper "light".

[Janglin_Jack]

It sounds awesome. Mercury super reverb OT. 6L6 with GZ34 recto. In 1x12 Deluxe Reverb chassis and cabinet with Cannabis Rex Mid resistor slightly higher than stock. A few circuit changes came about during my trouble shooting. .047 in PI a 10uf bypass cap on V2A. 47pf cap across PI plates. 820/100 ohm NFB circuit. Telecaster sounds awesome and my SG Classic with dual P90 just sounds monstrous. With volume at 8 or 9 it is growling with no pedals or booster. Will play at practice with my LesPaul and pedals and see how versatile it is.

This one sounds better than the one I made previously with a Tweed Bassman OT and 2x10 baffle.

Would love to be able to learn my scope better. I am sure I could have found this resistor faster with more experience.

[Lefty Lou]

It sounds awesome. Mercury super reverb OT. 6L6 with GZ34 recto. In 1x12 Deluxe Reverb chassis and cabinet with Cannabis Rex Mid resistor slightly higher than stock. A few circuit changes came about during my trouble shooting. .047 in PI a 10uf bypass cap on V2A. 47pf cap across PI plates. 820/100 ohm NFB circuit. Telecaster sounds awesome and my SG Classic with dual P90 just sounds monstrous. With volume at 8 or 9 it is growling with no pedals or booster. Will play at practice with my LesPaul and pedals and see how versatile it is.

This one sounds better than the one I made previously with a Tweed Bassman OT and 2x10 baffle.

Would love to be able to learn my scope better. I am sure I could have found this resistor faster with more experience.

40 watts + Class AB does the job for most (small/medium) venues. I could be perfectly happy with using nothing more than 40 watt Fender and 50 watt Marshall amps all day long. I like cranked, but I typically drive an amp semi-hard and use a good OD combination. I do like 5881 Tung Sols, KT66 Saratovs, Philips ECG 6L6WGB, TAD 6L6GC-STR and 6L6WGC-STR tube sets in 40 watt Fender tube amps. * FWIW in the larger scheme of things, your MM Super OT does more to contribute to the overall increased headroom and soundstage presence that your new amp exhibits.

[Janglin_Jack]

Something is up. Smelled hot and the chassis was hot. PT was hot. Never re biased after some of the changes I made. the chassis on the PT side was way too hot. Seems like it was the recto tube but need to check the voltages, etc. amp sounded awesome BTW!!, played it 4 hours. Hopefully all is OK

Mike

[Lefty Lou]

Something is up. Smelled hot and the chassis was hot. PT was hot. Never re biased after some of the changes I made. the chassis on the PT side was way too hot. Seems like it was the recto tube but need to check the voltages, etc. amp sounded awesome BTW!!, played it 4 hours. Hopefully all is OK

Mike

What is the amount of static plate dissipation you prefer to set your bias to? I like 65% typically if I can get away with it. Some modern tubes like Tung Sol's 5881 can take higher plate voltage for longer play periods although it's still best if you stay within acceptable tube data sheet limits. A Mullard GZ34 and a few long black plate 12AX7's would be a fitting tribute/contribution to your sound and to your amp.

[Janglin_Jack]

Something is up. Smelled hot and the chassis was hot. PT was hot. Never re biased after some of the changes I made. the chassis on the PT side was way too hot. Seems like it was the recto tube but need to check the voltages, etc. amp sounded awesome BTW!!, played it 4 hours. Hopefully all is OK

Mike

What is the amount of static plate dissipation you prefer to set your bias to? I like 65% typically if I can get away with it. Some modern tubes like Tung Sol's 5881 can take higher plate voltage for longer play periods although it's still best if you stay within acceptable tube data sheet limits. A Mullard GZ34 and a few long black plate 12AX7's would be a fitting tribute/contribution to your sound and to your amp.

Checked the voltages last night and everything looked OK. I am getting 450v on the plates and using EH 6L6GC. 30x.60/450=40mA. When I check the bias, it was over 47mA - almost 50mA!! Yikes. I guess I was running them hot, (at or over max plate dissipation)! Will recheck one more time tonight, but it should be down around 38mA on one tube, and around 40mA on the other. I guess that is right around 58-59%??

Mike

[Lefty Lou]

I'm not up on the Electro Harmonix line of output tubes but, apparently they're capable of holding their own at a higher static plate dissipation although you wouldn't want to gamble on it for too long. Should you ever desire to rotate your 6L6's, I've tried the TAD 6L6GC-STR which are, "the perfect choice for the tone of the rock legends. The TAD 6L6 GC-STR has a tight low end and has all the guts and bite to perfectly accomplish all the rocking sounds from SRV to modern NU-Metal. They have powerful deep bass and a clear, airy top end.

This TAD 6L6GC-STR combines the famous reliability of the American made Philips/Sylvania STR series, and the beefed-up black-plate system of the highly regarded vintage RCA 6L6GC tube. The best of both worlds! Silky top end combined with deep bass response and lots of headroom make this 6L6 tube a living classic.

The TAD 6L6GC-STR has an exclusive black-plate design, gold grid wire, double getter construction, no-noise filaments, and a 1.2mm thick heavy duty glass envelope." - The Tube Store

I also like the TAD 6L6WGC, Tung Sol 5881, JAN/Philips 6L6WGB, and KT66 (Valve Arts or Gold Lion). My buddy has a NOS Groove Tube Saratov KT66 set in one Fender SFSR and a TAD 6L6GC-STR in another Fender SFSR amp. Both sets sound stupendous however I really like the KT66's. The only thing is that you have to monitor you PT's filament voltage prior to installation of the KT66's.

[Janglin_Jack]

LLou, thanks for the tip on the TAD. Will get a set the next time I order tubes. I have KT66 in my JTM45

Mike

[Lefty Lou]

I had my buddy Chris's (2) Fender SFSR amps flipped (meaning) what I thought to be the amp with the GT KT66's was actually the one with the TAD 6L6GC-STR matched pair. I was really surprised when I plugged my SG into the TAD 6L6GC-STR SFSR amp yesterday evening because it was so beefy and powerful (w/o boominess) and yet balanced in the mids and highs. The amp sounded like the best cross between a Marshall and Fender amp, I absolutely loved it.