microphonic wires V4 in a fender Deluxe

Steve Waltz · From: USA

This Deluxe has quite a bit of white noise on the reverb channel. The other channel is clean. All electrolytics are new. All of the tubes are new. The volume pot is a pull type. It is hard to turn and it's noisy as it turns. I use pot cleaner and it didn't help much. Using a chop stick I found that pin 3 or 4(I can't remember right now)on V4 was microphonic and the wire attached to it is as well. The wire is microphonic for at least three inches before it goes to the reverb RCA connection point on the back of the amp. The .1 600VDC cap that is attached to pin 3 or 4 is also slightly microphonic.

I ordered a new pot and a new sprague .1 600VDC. Am I on the right track? Any other suggestions. The pin in question doesn't crackel when touched with the stick like a bad solder point you can just hear it.

Thanks for the help again,

Steve

Ken Fox · From: Nashville GA USA

Look for the presence of DC voltage on the pots wiper (center terminal). If there is DC, you have a cap leaking DC in the tone section of channel 2. That would also account for a very scratchy pot that will not clean up!

Also you should change the emitter bypass cap on V4 (25uf at 25WVDC)! That is at pin 3 and 8! It can get microphonic and cause the amp to eventually cause a feedback tone at 1000Hz or so. It can near deafen you!!

[This message was edited by Ken Fox on 16 February 2006 at 11:56 AM.]

Steve Waltz · From: USA

Ken,

How do I check for DC leakage on the pot. Do I set my multimeter for DC volts around 500 or less, ground to chassis and then attach the lead to that wiper? Should there be no DC? Or a little based on the % amount of of the caps? Sorry for the basic questions but you know I'm still learning.

I've been trying to measure leakage on the caps and I'm not getting very far.

steve

Ken Fox · From: Nashville GA USA

Do as you said with the meter. Should be less that 0.5 vdc! Then you can check each cap to find if there is DC on both sides of the cap. There is DC on one side only, blocked on the other side

[This message was edited by Ken Fox on 16 February 2006 at 11:59 AM.]

Steve Waltz · From: USA

One more.....

If there is DC leakage it's a cap because caps pass AC but not DC? Check each cap for leakage?

Steve

Ken Fox · From: Nashville GA USA

Yes, they pass AC only

Steve Waltz · From: USA

Sorry, you got back to me while I was posting. Thanks for the help. I'll give it a shot tonight.

Steve

Steve Waltz · From: USA

I'm still looking for a fix on this amp. I checked the pots for DC and some of them have more than .5 VDC. I changed out the .1 600 VDC since that seemed bad but it is still there. I pulled the legs of the caps close to the pots to check for DC and on the cap that goes to the phase inverter it made a loud pop sound when I attached my meter to it. I couldn't get a reading. On an other cap the meter just went haywire and would not stop at a reading. Help! I can't figure out which cap is causing the trouble and I don't want to replace all of them.

I turn on the amp and let the tubes heat up, I then turn on the standby switch and for about ten seconds the amp is clean sounding and then the scratchy hiss starts to kick in like a volume knob was turned. That made me wonder if the problem is a resistor? What would heat up after the standby was turned on that would cause this noise?

Thanks,

Steve

Brad Sarno · From: St. Louis, MO USA

Steve. Have you replaced all the 100k preamp tube plate resistors? It sure sounds like a resistor problem. My guess is that it's a resistor in the B+ circuit, like the plate resistors since they don't see power until you turn the stand-by on to "run".

Brad

John Daugherty · From: Rolla, Missouri, USA

Just because the tubes are new, does not mean they are good. Have you cleaned the tube sockets? You can do a fairly good cleaning job by putting contact cleaner in the socket and inserting the tube several times. In some cases, the sockets and tube pins do not mate. You can bend the tube pins slightly to make the tube fit tighter.
All the advice on capacitors is good advice. Replacing all of the coupling caps(cap connected to the grid of each tube) is a good idea.

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J Fletcher · From: London,Ont,Canada

I second what Brad said. Sounds like a noisy 100k plate resistor, at least judging by the description of the noise and when it starts...Jerry

Steve Waltz · From: USA

Thanks for the help. I replaced about four of the 100K resistors and it didn't help. I'll try to do the rest. I was reading in my book about fender amps from the guy that builds "Thunderfunk" that the 100K resistors should only be replaced with Carbon Comp. I can't get those here in oakland. I can get high quality resistors that are flame proof and I think they are carbon film. Any tone problem with that? They are supposed to be more quiet and longer lasting. I'm saving the old ones just in case.

I already cleaned all tube sockets and retentioned everything. No noise when moving any parts, only the microphonic wires on V4.

So I'll do the rest of the 100K resistors and order the rest of the caps.

Thanks,
Steve

Brad Sarno · From: St. Louis, MO USA

Any type of 100k will work if you want to test it and see if that fixes it. However, many people, including myself, believe that there is a tonal goodness with carbon comp resistors when used in high voltage B+ locations. They are a bit noiser but for guitar use, it's neglegible. On the plate resistors in my Black Box and Rev Preamp I use carbon comp. All the other audio resistors are nice Vishay/Dale metal film types or ceramic power types where needed. In my Fender amps, I use carbon comp everywhere except at the power tubes where I like the flameproof types. Some argue that the tonal differences in resistors really shows up when there is high voltage across them. That's why the plate resistors should be carbon. I notice a warmer, more "furry", less hi-fi sound with carbon comp. Metal film in those positions can sound a bit too clean and sterile. For signal path resistors and cathode resistors I like the film types. Depends on the purpose of the device though. If it's a guitar amp made for dirt, I like carbon almost everywhere. If it's a hi-fi stereo, then pretty much film everywhere. If it's a steel guitar device I like a balance of both types.

I'd recommend replacing the rest of the 100k's and see if you fix it. If not, then keep going. I still have a strong feeling that your problem is a bad old resistor somewhere. That is if it's not a tube.

Keep us posted. It's often these kinds of troubleshooting sessions that I learn the most from.

Brad

Les Pierce · From: Shreveport, LA

I played an early '70s Deluxe for years, and at least once a night had to rap it on top to stop it from "singing". It always seemed to be in preamp tubes, as just flicking them with your finger caused a lot of popping in the speaker, and replacing them stopped it for a while.

I thought it gave the amp personality!

Les

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Strat,Tele
Dekley S-10

John Billings · From: Ohio, USA

You might try foolin' around with the way the wires are routed.

Steve Waltz · From: USA

I haven't fixed this Delux yet but my vibrosonc was having a similar problem. It has new JJ tubes. After just about giving up I changed out the reverb tube in V4 and put an old one in......and yep that did it. Live and Learn. New tubes can be bad from the box. I also had to move some wires around to kill a litle noise and now it's fine. All new caps helped too I'm sure.

I'm going to change the tubes in the delux tonight and see if that works for that amp as well.

BTW.. I replaced a few of the non electrolytic caps in the vibrosonic. Those are the ones on the board in the .1 600VDC and .047 range. I tried some of the expensive ones to see if there was a change. I wanted just a little more clarity in the tone. I changed out the mid range on the reverb channel with a Hovland cap and it seems to have made a difference. I going to order some more of the "Anglea" caps and try those out. I think for steel these high end caps are making a difference and yet I still hear all of the good things about the amp. I'm going to change the spring reveb out to a three spring for a longer decay next. That is only a $30 part. If I have time I'll record the one vibrosonic that is stock and this one and see if I can post it so that people can hear if there is a difference.

steve

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