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May 17, 2024, 07:08:47 PM

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#2
Amplifier Discussion / Re: Randall RG100HT Weak Chann...
Last post by g1 - Today at 06:08:45 PM
Since you already replaced Q2, next suspects would be C7 or Q3.
#3
Amplifier Discussion / Peavey Bandit 65 transformer
Last post by mr.death - Today at 05:31:22 PM
Hi, Recently I was given an old peavey bandit 65 amp with issues. I replaced the old electrolytics and in the process some solder dripped across the board bridging some traces. I turned the amp on not knowing and fried the transformer as a result. I need a replacement transformer but am having a hard time finding one thats not bloody expensive. What criteria needs to be met when looking for a new transformer? Can I buy not peavey branded, generic? The part number for the fried part is 70518713.
Thanks
#4
Thanks for the tip.
#5
Amplifier Discussion / Re: Randall RG100HT Weak Chann...
Last post by g1 - Today at 02:23:42 PM
The link you posted is not working.  Try to attach your picture directly.  When you respond to this post, click the 'preview' button and you will see the option to attach a file.
#6
Preamps and Effects / Re: Joe Davisson's Vulcan prea...
Last post by Umlaut - Today at 05:25:31 AM
Well I breadboarded it early this week out of curiosity. A few observations:
- 18V instead of 9 does not make much difference.
- bias is finicky, get as close to 4.5V as possible (using 2 resistors in series or a trimmer).
- while the voicing of this circuit is not exactly to my liking, it is undeniably well designed: tried other coupling caps, bypass caps and so on, and it quicky went south. Only tried stuff for about 20min, though.
- snubber caps collector-to-base -> Nope. A 2.2n cap across the last collector bias resistor worked MUCH better to tame the highs.
- somebody at DIYStompboxes suggested using other diodes. I tried BAT85 and it sounded pretty good.

I will have to revisit it at some point during summer, as it definitely has a nice vibe. Hope this helps!
#7
Schematics and Layouts / Re: Keelhauler MKII - a reason...
Last post by Umlaut - Today at 05:18:41 AM
Wish I could, but all my recording gear is on the other side of Europe now and I won't be able to access it until christmas at earliest  :-[  phone recordings don't do it justice, unfortunately. I might build one in a stompbox and send it to a mate to test it and record some clips during summer, we'll see...
#8
Schematics and Layouts / Re: Keelhauler MKII - a reason...
Last post by joecool85 - May 16, 2024, 02:45:31 PM
Looks interesting. I'd love to hear some clips!
#9
Amplifier Discussion / Randall RG100HT Weak Channel 1
Last post by Randy Lahey - May 16, 2024, 12:20:37 PM
Hi all,
I have a Randall RG100HT amp head that has a really weak/quiet Channel 1 (not Input 1).  Channel 2 sounds great and is loud as I would expect for a ~100W amp.  When using Channel 1, I have to turn the gain and volume up (past 12 noon) to get a decent signal and even then, there's not much definition to the audio and it is somewhat muffled.

I have reviewed the schematic, confirmed component values, checked DC voltages within the Channel 1 circuit, and ran a signal through Channel 1 and scoped it along the audio path.  I have 24v DC along the DC rail and have good AC audio signal up to the gate of Q2.  All components are within spec and I have replaced Q2 with a new 2N5484 transistor.  Attached is the schematic for Channel 1 and I have annotated it (in blue) with measured DC voltages.  The DC voltages for Q1 are within spec but those at Q2 and Q3 seem to support the notion that something isn't right at either Q2 or Q3.

I'm more familiar with tube amps and not SS amps so I may be not recognizing obvious solutions - so I'm putting this problem to the forum.  What recommendations do you have as a solution to the weak audio in Channel 1?https://photos.google.com/photo/AF1QipM9NMuHgN6irIVMYvnkxXqrwgm2pGozITmv5MDl
#10
Amplifier Discussion / Re: Repairing a Gibson G-105 G...
Last post by DrGonz78 - May 15, 2024, 11:01:19 PM
List voltage reading for Q8 & Q9 at  all pin's connection points. Measure all power supplies. What are your -/+40v rails? -/+12v rails? Can you scope a signal through the unit and figure out where the signal goes bezerk?

Edit: If you scope the output is the fuzz actually crossover distortion?