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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Fri Feb 03, 2012 6:45 pm
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I'd try resoldering the components hanging off the culprit jack. And see what happens. If it still makes noise, try another resistor. Also, check the wiring (coax, I assume). You may have the inner portion touching the outer shielded portion, somewhere.

Good luck! Keep us posted.


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Fri Feb 03, 2012 7:04 pm
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BMW2002Ti wrote:
I'd try resoldering the components hanging off the culprit jack. And see what happens. If it still makes noise, try another resistor. Also, check the wiring (coax, I assume). You may have the inner portion touching the outer shielded portion, somewhere.

Good luck! Keep us posted.


Going to go eat dinner now, but I will try resoldering the resistor.

The wire is just plain wire, not coax. I did bend both resistors further away from the other wires and terminals which might have helped a little. It is hard to tell.

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Fri Feb 03, 2012 10:03 pm
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Ok. I have reflowed the solder on all of the connections of all four input jacks. I have also tried to tighten the contact between the tip and switch terminals of all four jacks. I also redressd a couple of wires to get get them away from the soldered eyelets.

The amp has been sitting idling for about 2 hours now. There is still a very slight crackle/scratchy noise riding on the background hiss, but both the crackle and the hiss seem to be reduced and the crackle is not occurring with as great a frequency as it was before. I'm not sure what else I can do inside the amp to improve things or if I should just declare victory and live with the slight noise. The parts for the presence pot mod arrive next Tuesday and I will install them next weekend. I'll see if that has any impact on the noise and take a look around inside the amp again. I'm also going to plug the amp into a different outlet to see if possibly my power conditioner is causing the noise.

Any other suggestions?

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Fri Feb 03, 2012 10:37 pm
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Plugging directly into the wall outlet insead of my power conditioner made no difference.

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 04, 2012 1:18 am
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Blues, I'm wondering which pre amp tubes you're using. Are they NOS GE's? And yeah, you've got the real line on that presence circuit! Appologize if I missed something here, but that's a bunch of pages. Actually your tap test sounds reasonable to me, a voltage pop test would probably turn up the same results, just MHO. Art

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 04, 2012 6:30 am
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aclempoppi wrote:
Blues, I'm wondering which pre amp tubes you're using. Are they NOS GE's? And yeah, you've got the real line on that presence circuit! Appologize if I missed something here, but that's a bunch of pages. Actually your tap test sounds reasonable to me, a voltage pop test would probably turn up the same results, just MHO. Art


V1 is a NOS JAN GE 12AY7. V2 and V3 are new JJ 12AX7s.

What is a voltage pop test?

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 04, 2012 7:18 pm
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Ok. Here is my little demo. Please accept my apologies in advance. :lol:

http://www.youtube.com/watch?v=sio3jHx-cKQ

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 04, 2012 7:26 pm
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Bluesky, I couldn't really hear the crackling noise on top of your background hiss. Prolly my crappy computer speakers. :( I'd try replacing that 1meg ohm & maybe the two 68k-ohm resistors off the input to the grid or the first 12AX7 (or 12AY7).

Good luck!


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 04, 2012 10:33 pm
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BMW2002Ti wrote:
Bluesky, I couldn't really hear the crackling noise on top of your background hiss. Prolly my crappy computer speakers. :( I'd try replacing that 1meg ohm & maybe the two 68k-ohm resistors off the input to the grid or the first 12AX7 (or 12AY7).

Good luck!


The crackling noise is pretty much gone now. It was really obvious before. It sounded like popcorn. Now you have to get right up to the amp to hear it. Tapping things no longer causes the amp to break out in a fit of crackles. I'm going to leave it be for now and just keep an ear on things.

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Sat Feb 04, 2012 10:55 pm
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Yeah... letting sleeping dogs lie prolly best.

Enjoy the amp :D


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Mon Feb 06, 2012 4:24 pm
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Blue, you got this amp doing good things, right? Gigging with it? I forgot if you already posted the final verdict. My short-term memory is kinda.... wait... I forgot what I wanted to say. :?:


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Mon Feb 06, 2012 5:28 pm
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BMW2002Ti wrote:
Blue, you got this amp doing good things, right? Gigging with it? I forgot if you already posted the final verdict. My short-term memory is kinda.... wait... I forgot what I wanted to say. :?:


Did you see my little demo that I posted earlier?

http://www.youtube.com/watch?v=sio3jHx-cKQ

I don't gig. I'm just a home player. The engineer in me wants to build things that the guitar player in me can play. My instructor tried the amp last week and loved it. I have offered him the use of both the 5F6A and my modded Champion 600 for his next CD and he has accepted. I'm going to ask him to record a short demo on both for me at my next lesson.

The parts to mod the Presence control from the 59 style circuit to the modern circuit (gets rid of the DC noise when the pot is turned) should arrive tomorrow. I will be able to just build up the new pot, remove the old one and the cap, and drop it in. When I do that I will also check and maybe up the bias a little bit to try and get a slightly earlier breakup. I have my eyes on a set of NOS JAN 5881s from KCA NOS Tubes for my birthday (April 2 in case anyone wants to buy them for me. :lol: ). Either this pair

https://www.kcanostubes.com/content/nos ... s-quartets

or this pair

https://www.kcanostubes.com/content/nos ... vania-5881

My plate voltage runs about 432 VDC so Mike has said that either pair will be fine. Mike Kropotkin, the owner of KCA lives about 20 minutes from me. He posts a lot on TGP. I have met and talked with him and found him to be a lot nicer guy than he sometimes comes across as on TGP. :lol:

The crackling/scratchy noise has been greatly reduced in both volume level and frequency of occurrance. I'm happy with it now. The hum level of the amp is about the same as that from my BDRI. The background hiss is just slightly higher than the BDRI. I can live with all that. Once you hit the first note, all other noises are forgotten.

I am now working on tweaking the amp settings for best tone. The tone controls on the 5F6A don't seem to interact as much as those on the BDRI. The stacks are similar but with some different values for the $@!&# resistor, bass cap, and pot curve. The tone stack insertion loss on the 5F6A seems to be less than that of the BDRI, probably due to the low impedance output cathode follower driving the tone stack and the tone stack driving the high impedance input of the PI.

I have a Boss FRV-1 reverb pedal which is actually a really nice pedal. Using Boss's COSM technology it really gets close to the sound of Fender's standalone reverb unit (I'm thinking that might be my next build. :D ). It is interesting to note that the FRV-1 outputs a pretty constant level of hiss that does not vary with the control settings. For some reason, the 5F6A reacts more to the hiss from the FRV-1 than the BDRI does and displays a higher overall hiss level with the FRV-1 than the BDRI even though their residual hiss levels are very similar. The only thing I can figure is because I am jumpering the Normal and Bright inputs together on the 5F6A which is probably resulting is a bit higher gain than the BDRi preamp exhibits.

The bottom line is, this is a fantastic amp. Compared to some original 59 Bassman demos I have found on YouTube, it's sound is very close. Not exactly the same but given 50+ years difference in manufacture, close enough to do the job. With just a few exceptions that I noted in my build up, parts quality is excellent. A good set of tubes is definitely a worthwhile investment. Even though the kit does not have any instructions, just a schematic and wiring diagram, I think most people who have worked on tube amps before and are competent with a soldering iron, could build it. One just needs to take their time. Hopefully my narrative will serve as a suitable guide to someone contemplating building this or a similar amp.

Whew! Sorry I rambled on for so long. :lol: I've got a real bad migraine and am getting ready to eat dinner after which I will probably go to bed. No guitar playing tonight, I think. :cry:

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Mon Feb 06, 2012 5:58 pm
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Good you got the puppy going in the right direction. I like original US made TungSol mil spec 5881/6L6WGB. I have not tried the re-issued Russian made ones.

I bias mine to around 19-21 idle watts per tubes.

http://www.ebay.com/itm/Match-Pair-Tung ... 3f132f650b


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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Mon Feb 06, 2012 8:47 pm
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BMW2002Ti wrote:
Good you got the puppy going in the right direction. I like original US made TungSol mil spec 5881/6L6WGB. I have not tried the re-issued Russian made ones.

I bias mine to around 19-21 idle watts per tubes.

http://www.ebay.com/itm/Match-Pair-Tung ... 3f132f650b


5881/6L6GBs are 25 watt tubes. That's around 80% max dissipation. Kinda hot don't you think?

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Post subject: Re: My Weber 5F6A Bassman Build-Up Thread
Posted: Mon Feb 06, 2012 10:04 pm
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Not for the real, NOS mil spec TungSol (or any other 1950-60's 5881). TS is notorious for under-rating their tubes. They recommend no more than 350VDC on the plate. Really, they've been tested to 500 VDC and 26 watts per tube. Much tougher than a "regular" 6L6GB, which RCA recommends to set at 19 watts per tube, push-pull, Class AB1 setting.

You maybe thinking the older Bassman 5B6 and 5C6 circuits which ran the 6L6GB or 5881 in cathode-biased, Class "A" mode. Then, you'd have a limit of about 12-15 watts per tube.


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