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Messages - g1

#886
Amplifier Discussion / Re: Ibanez TBX150H got real quiet
December 31, 2013, 11:44:30 AM
  Sometimes just giving those jacks some exercise will fix the problem.  Plug your cable in and out of those jacks a dozen times or so, see if that helps.
Usually you also need to spray some contact cleaner in them (something like deoxit or nu-trol) as well as exercising them to work the cleaner in.
  The other option is to just leave a short patch cable in there.
#887
This is the article on negative feedback with op amps:
http://www.allaboutcircuits.com/vol_3/chpt_8/4.html
I don't think it appears on the mouser website although they may have a link to it.
#888
Amplifier Discussion / Re: Kustom "Frankenstein"
December 18, 2013, 11:31:22 AM
  Thanks JM, you're right, the goop in my "parts cleaner" pail is probably mostly oils now and very little kerosene.  It may not evaporate as fast as some other fuels, but that doesn't mean it doesn't evaporate.  I guess the key is to wipe off as much as you can and the rest should evaporate.
#889
For byproduct I think he means the preamp IC rails after the 1K droppers.  In the stock Lead 12, main rails are +/-19, IC's +/-16V.
  So with 24V rather than 28V transformer, main rails approx. +/-17, IC's +/-14.
Am I close Dr.Gonz?
#890
  I would not recommend plugging the 100V amp into 120V.  If any of the caps operate near their voltage rating, the extra voltage may be too much for them.
If you could use a variac and check them, you may get away with it, but the amp will now be capable of producing more power which could strain the transformer.
As far as the transformer swap, the lead 12 runs on +/-19V, where the MG10 runs on +/-15V, so  the transformers are not the same.
#891
Amplifier Discussion / Re: Kustom "Frankenstein"
December 16, 2013, 10:57:19 PM
  What a coincidence, I was just breaking out the alcohol too!   ;)
Looks like restaurant/bar grease/nicotine type residue, probably was in the same place for a long time.
  Dr.Gonz:  as far as the kerosene goes, I don't think it evaporates so I wouldn't recommend it.  I filled a pail with some and forgot a motorcycle chain in there about 5 years ago, no lid and the pail is still full.
#892
 There is some speculation it may be similar to Vox Escort 30 due to the Dallas Music connection.
Does the schematic match up?
#893
Amplifier Discussion / Re: Peavey 212 Classic VT Series
December 13, 2013, 02:07:28 PM
 Have you tried cleaning and resoldering the mid pot yet?  If so, what was the result?
#894
  Any idea what the resistor goes to?  Looks like some regulators on that board?  Also some jacks?  You've probably checked for a simple problem, but this schematic may be close:
http://music-electronics-forum.com/attachments/23732d1370622849-spider-iii-1508-3012-hd75.pdf
  I would think most of those amps blow the power amp and get gutted, so the boards could be good, on the other hand it would depend on whether the seller was parting out amps or came across a pile of junked defective boards, in which case they could ALL be bad.
#895
  Do you have experience (and tools/test equipment) fixing amplifiers?
Schematic is available here:  http://elektrotanya.com/hughes_and_kettner_matrix_100_amplifier.pdf/download.html
#896
 With inexpensive practice amps, it is not uncommon for the circuit boards to be secured only by the pots.  Often what happens is the amp falls on it's face while there is a cord plugged into the input jack.
This often causes the board to bend and breaks the pots.
Inspect the input jack to be sure none of the solder joints have cracked.
The best way to check if some pots are good is with DMM measuring ohms.
Also you can look with a magnifier to see if the carbon track is cracked (in the same area where the bad pots are cracked).
#897
Tubes and Hybrids / Re: 18W Amp Build - Few Minor Issues
November 15, 2013, 11:27:23 AM
  Most of the picoscopes can only handle small voltages (20V or less?) so if you are wanting to work on tube amps you will probably need 100:1 probes.
  Recommend doing further research on their limitations before you purchase one.
#898
+/-15.7V does not sound right for the supply rails, unless you are talking about the low voltage supply.  The power amp should be running on higher voltages than that.
Without a schematic there is not much anyone can suggest.
  The schematic does not seem to be available online unless you buy it here:
http://www.majelectronic.co.uk/
#899
1)  A switching jack (cliff) was wired in SERIES between the Fender combo amp and it's speakers.  It was wired up to be an input to the speakers, NOT an output from the Fender amp.
  This enabled the Fender combo's speakers to be used as if they were a separate speaker cab.
2)  The Fender speakers were re-wired so they would be in SERIES (16 ohm).  The stock wiring had been parallel (4 ohm).
This was because the Vox amp had an extension speaker jack that was rated for 16 ohms, and the Fender speakers were to be used as an ext.spkr. for the Vox amp.
#900
  Not sure what you could do to increase the reliability, sorry.
But I will mention that before you connect the new chips, the power supplies in the amp must be fully discharged.
  Otherwise you can blow the brand new chips before you ever turn the amp on.