Author Topic: Intermittent problem w/ F-2B (was: How do I open ..) (Read 500 times)

David Houck · « **on:** December 08, 2005, 10:03:02 AM »

In a previous thread, I reported that when I first plugged in my new (to me) F-2B, the first channel wasn't working. I had exercised the jacks and knobs but to no avail. The second channel works great. Well I just now plugged into channel 1 and now it's working fine. Perhaps the problem is intermittent. In the previous thread it was suggested that I check the tubes. So I've set the unit on my workbench and I'm looking at all the screws and I'm thinking it might be helpful if I ask which screws I'm supposed to take out to open up the preamp.

gtrguy · « **Reply #1 on:** December 08, 2005, 11:11:22 AM »

I undo the top two and the three on the back and the top opens on mine. Check the condition of the foam and replace it if it is shot. I'll also run a pistol cleaning brass brush (9mm) in my inputs to clean them with a little rubbing achol.

David Houck · « **Reply #2 on:** December 08, 2005, 11:28:16 AM »

Thanks David, those were the screws I needed!

David Houck · « **Reply #3 on:** December 08, 2005, 11:54:08 AM »

On each tube, there are four points that glow. On the tube closest to Channel 1, one of these points was not glowing as bright as the others. I switched tubes and checked again; the same spot on the same tube was still not glowing like the others. With the tubes switched, I put the top back on and plugged it back into the rig. Channel 2 is still fine; Channel 1 still has an intermittent problem. I sprayed tuner cleaner in the jack and exercised it 30 times; but that didn't help. Then I realized that when the first jack of Channel 1 isn't working, neither is the second jack of Channel 1; thus I don't think it's a problem with the contacts or even the jack. And my guess is that switching the tubes should have moved the problem to Channel 2 if it was a tube problem. So I'm thinking it's not the jacks and it's not the tubes.

spose · « **Reply #4 on:** December 08, 2005, 12:09:35 PM »

while you're in there...
how are the filter caps looking?

are they secure to the board?
is the foam intact?

David Houck · « **Reply #5 on:** December 08, 2005, 01:05:36 PM »

The caps looks fine and feel secure; and the foam looks fine. Here are some pics for your enjoyment.

gtrguy · « **Reply #6 on:** December 08, 2005, 01:40:49 PM »

Have you tried cleaning the contact switch that goes with the jacks? A matchbook striking surface might clean it. However, I can't remember what they do right now.

David Houck · « **Reply #7 on:** December 08, 2005, 01:55:57 PM »

David; it appears to be the case that they are either both working or both not working, which would seem to me to rule out the contact switches. But I might as well try and clean them; it certainly won't hurt.

kmh364 · « **Reply #8 on:** December 11, 2005, 06:40:28 AM »

Dave:

Just for sh*ts and giggles, you might wanna try re-tinning all the solder joints on the pc board, jacks, sockets, etc. Sometimes you get a cracked or cold joint and a re-tin will fix the problem. While you're at it, you can tighten every mechanical fastener in the thing and make sure all your grounding/bonding is continuous. Look for any obvious signs of corrosion at any connection (electrical or mechanical), especially chassis grounding points and the chassis fasteners themselves. The chassis must be all at the same ground potential or noise current and/or intermittent operation will result.

David Houck · « **Reply #9 on:** December 12, 2005, 05:54:34 AM »

Kevin; I don't have the skills to do the re-tinning. As posted in another thread, I used the F-2B at my gig Friday night and it sounded pretty good. So now I'm hesitant to take it out of the rack! However, my next step will probably be to take it to the local amp guru and have him check the circuits.

kmh364 · « **Reply #10 on:** December 12, 2005, 06:04:57 AM »

Well, your amp guy should be able to get it ship-shape for minimal cost.

I take it you're impressed with the sound of your F-2B as compared to your F-1X, despite the little glitch?

David Houck · « **Reply #11 on:** December 12, 2005, 06:08:03 PM »

Actually, I haven't even used the F-1X since I got the F-2B. But, they are significantly different and I think it is going to be the case that I will value each equally. I think there are songs we're doing that work better with the F-1X; and there are songs that work better with the F-2B. So at this point I can't say that I prefer the F-2B; I miss not being able to get the clarity of the F-1X. But the sound of the F-2B is something that I've been looking for on certain songs, but couldn't get from the F-1X. I'm certainly leaning toward getting an A/B switch! But my rig sure is getting more complex.

David Houck · « **Reply #12 on:** March 05, 2006, 05:54:49 PM »

Well, a couple weeks ago I finally got around to taking the F-2B to the Amp Doctor; and I told him about the intermittent problem. I got it back Friday. He said he couldn't get it to be intermittent; but he did say that the tubes were bad, so he replaced the tubes. I got it home and plugged it up; and immediately it was intermittent. However, after only a very short while it started working fine. I practiced for a while and then Keith H came for a visit and we played through it for several hours. Only near the end of Keith's visit did it start to be just a little bit noisy. Saturday it worked fine and this morning it worked fine. So at this point I don't know what to think. I guess I'll just continue to see how it goes.

dfung60 · « **Reply #13 on:** March 05, 2006, 07:08:40 PM »

Hey, based on your 3/5/06 post, it sounds like the intermittent problem may be in your power amp or the interface between the two. Time to try a different power amp with the F2-B or do a check on cabling.

It's often hard to reproduce intermittent failures like this apart from your full rig (or even with it).

Tube power amps often have intermittent failures like you're describing when the power supply capacitors go bad. The F2-B has large power reservoir caps as well and they could go bad, but, since the power demands of a preamp are so low compared to a power amp, it's unlikely that this is the problem.

My two cents,

David Fung

David Houck · « **Reply #14 on:** March 05, 2006, 08:04:35 PM »

My guess is a cap too. However, over the last couple of months I haven't used the F-2B, only the F-1X, and I haven't had any problems; so it's not the power amp. The problem only occured with the F-2B, and then only the few times I used channel 1; channel 2 was fine.