Can anyone explain parts in '64 Vibrolux Reverb?

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9/4/2000 11:15 AM

Carl

Can anyone explain parts in '64 Vibrolux Reverb? Hello anyone,     I'm unable to locate a schematic for this Vibrolux Reverb Model AA864 (stamped "NJ" on tube chart) and request your help on some clarification.     I'm not an amp tech so please forgive me if I'm confusing. The chassis looks very clean and the solder joints appear to be untouched. I notice that some of the components are a bit odd compared to most other blackface amps and was wondering if anyone could tell me if what I have listed are original parts?     (1.) The coupling (or bypass?) caps for the pre-amp and reverb tubes are usually 25uf 25v, but in this amp they are small and silver (like Spragues) with "PCM 35v 22uf" written on them in black letters.     (2.) Instead of a 25uf 25v cap going to pin 8 on the vibrato 12ax7, there is a 2mf 25v Astron Minimite cap.     (3.) There are two resistors (100k, 1m) soldered in parallel which go to pin 6 on the phase inverter 12ax7.     (4.) The main power transformer has plastic leads instead of cloth leads. On the top of the transformer (inside the chassis), "B4064" is stamped in silver. On the bottom, it reads "C.S.A. TEST" "125P26A" and "606402." The red, green and yellow plastic leads say "CANADA" on them.     Thanks for your time!

 

9/4/2000 9:34 PM

Tim Gagan

Hi Carl,     The parts you mention must be replacement parts. It's generally easier to find--especially in the days before the Internet and the big revival in tube amp hobbyism--22mfd caps than 25mfd, so the 22's are often used to replace the 25's (which are bypass caps). I don't know why someone would put a 2mfd cap on pin 8 of the vibrato 12AX7, but if the vibrato works, it should be fine. If the bypass caps in the vibrato circuit aren't good or too low a value, the vibrato won't work.     As for the 100k/1meg resistors in parallel, they combine for a value of about 90k. Fender generally has 100k in that position. Are the 100k/1M in addition to the 100k, or was the 1M added across the standard 100K? Maybe somebody was trying to bring that value closer to the 82k that's usually on the other side of the PI, going to pin 1.     My guess is that the transformer is a replacement as well, although I couldn't say for sure.     Have you looked at the filter caps and the bias supply caps? If the bypass caps have been replaced, it's a good bet that the filter caps have been as well.     Tim

 

9/5/2000 12:53 AM

Carl

Tim,     Thanks for the reply!     The vibrato still works with the 2uf cap in place.     The 1meg resistor is in parallel with one 100k resistor (no other additional 100k). When I last checked them with a meter, they were not too far off their specified values. I tried removing the 1meg and got more highs/less lows.     The power transformer stumps me as the solder joints appear untouched. Yet, the leads are plastic? You're probably right about it being a replacement. The tech who worked on this amp did a good job. I know someone who has a '64 Deluxe Reverb (no logo model) and will check his transformer to see if it has cloth or plastic leads.     The filter and bias supply caps have been replaced with 22uf 500v caps and the solder joints are shiny unlike those inside the chassis.     I have ordered some 25uf 25v caps and want to make sure that they are the correct value before I install them.     Thanks again. Carl

 

9/5/2000 3:57 AM
Tim Gagan	Are you sure the bias supply cap is 22/500? It should be more in the 50mfd/100v - 100mfd/100v range. It's the electrolytic cap that's near the pilot light. Be careful if you replace this cap; because it's filtering negative vdc, it should go in backwards, with the positive side to ground.

 

9/5/2000 7:27 AM
Carl	Tim,     Excuse me, I'm not a tech. The filter caps underneath the amp inside the removable cover (5 ea.) are 22uf 500v. The cap below the pilot light is definitely the orig. 50uf type cap (the big one with brown paper like covering around it). Thanks, now I know where the bias cap is - it makes sense as it is wired to the bias pot. Carl

 

9/5/2000 2:44 PM
Bruce	Replace that bias filter one ASAP with a 68uF/100v e-cap.   It goes in with the + lead grounded.   Bruce

 

9/5/2000 9:47 PM

Rick Erickson

quote: "I don't know why someone would put a 2mfd cap on pin 8 of the vibrato 12AX7"     Reducing that 25uF cap to 2.2 or 4.7 uF eliminates the drop out of the oscillator when advancing the speed control. I regularly change this value when rebuilding a Fender amp.     Q{My guess is that the transformer is a replacement as well, although I couldn't say for sure.}     According to an article on Fender amps I recently read, Fender would mark prototype or experimental transformers with the word "test". BF amps had plastic insulation on the transformer leads also.   This is probably the original transformer in this amp.     RE

 

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