Vibrolux Reverb Maintenance and Mod Log

Date		Notes
11.12.04	Convert bias to a level adjust circuit per Hoffman article.	Left in 3.3k bias smoothing resistor between bias board and pot. Removed 100k resistor between bias pot and main board. Removed 100k resistor on main board; replaced with two 220k resistors
11.13.04	Replace filter caps	Sprague Atoms 16@475
11.14.04	Replaced all (6) bypass caps.	New Sprague 25mfd @25v electrolytics. All but 1 cap were 25mfd @25v – one was 5mfd @50v; replaced oddball 5 @50v bypass cap with 25 @25v.
11.19.04	Replaced two power tube coupling caps	Two .01 caps on the left side of main board - with orange drops 715
11.19.04	AA964 Blueprinting	- Replaced (2) 47k phase inverter plate load resistors to 100k on the left, 82k on the right. - Replaced (2)330k phase inverter cathode resistors with 1 meg metal film (AA270 SF schematic calls for 1 meg – but there were 330k in there!) - Removed .022 caps from power tube grids. - Changed phase inverter coupling cap from .01 to .001. <very much added treble/bright to amp> - Removed .002 cap from reverb input jack. - Removed 3.3k bias smoothing resistor. - Replaced bias range resistor with 470 ohm 3w carbon comp. - Bias circuit as described above and below. Left 15k resistor on bias pot (BF=27k)
11.20.04	Bias cap	Removed the (2) 70mfd bias caps and replaced them with one 100mfd @ 100v.
11.20.04	Coupling caps	.1 Mallory 150, (2) .022 Orange Drops, .047 Orange Drop.
11.21.04	Tone stack mod – both channels	Replaced .1 & .047 tone caps to .022 Orange Drops. 800v Mallory “Orange Drop” on Normal channel. Excellent mod – pulls out the lowest stuff only, leaves all the good stuff. Still big and thick.
11.21.04	Bright balance cap	Replace with silver mica 10 pf – the mica feels like it gives a rounder treble note. Maybe more musical than ceramic, but maybe not as organic.
11.21.04	Bright switch	Vibrato channel to silver mica 100 pf (from 120) This is a good mod.
11.29.04	Change phase inverter input cap	Back to silverface .01 value – better – got some of the beef back. Girthier.
12.10.04	Change phase inverter input cap	To .01 mfd Mallory 150, from Sprague Orange Drop. Excellent – surprisingly noticeable! Kept the beef, but tightened it up for sure. The .001 would probably be good with humbuckers
12.11.04	Tone stack caps	To Mallory 150, from Sprague Orange Drop. Went back and forth a few times. The ODs sound excellent, maybe a little looser in the mids/lows, but in a (mostly) good way. Could go with either one but the Mallory’s are a little more well-rounded.
12.11.04	Reverb area caps	Replace the .022 and .01 OD caps with Mallory 150. Noticeable tightening and woodifying to the mids – excellent.
Amp sounds killer. Loud and roasty, clean enough in the lows but still very beefy and big. Highs are excellent. Have all Mallorys except output coupling caps, 1 OD tremolo cap, OD normal channel tone stack (unused), and Mica bright caps. Still to do: - Possibly – swap orange drop output coupling caps with Mallory 150s - Swap out power supply (on filter caps) resistor(s) to BF values
12.18.04	Screen grid resistors	Replaced on power tubes with 470 ohm 3w metal film
12.18.04	Phase inverter cathode resistors	Replace current 1 meg metal film to 1 meg carbon comp
Jan 2005	Tubes	Tried the JJ 6L6 – good, but a bit strident, compared to the Winged C, which sounded fat and brown – went with the Winged C – very different bias values.