Help with Fender Vibrolux from 1980

[Disturber]

This is an 1980 blackface Vibrolux, same as an 1970's silverface but with the black faceplate. The last real Vibroluxes built looked like this, during the Rivera era.

I had to buy it. Don't know if I am keeping it, but it sounds damn good.

Any Fender experts here? (Alpep?)

It looks pretty untouched on the inside. What do you think? And that pot on the inside to the right, is that Hum balance or does it set the bias?

Anyone got a clue to what these speakers are? Eminence, CTS? They are only marked with "2858135".

Here is the beauty:

[Brewmaster]

I could be wrong but I don't think Orange Drops were used in these. The .1 Orange Drops in particular look like the newer ones. It doesn't matter though, they are correct replacements.

Hard to tell about that speaker but it does look original. 285 which are the first three digits, would mean it's a Rola.

http://www.unclespot.com/speakerEIAcodes.html

Get us a closer look at the board if you can and the pots. There are a few amp guys here that can help you out a little more.

Also, open the cap can on top of the chassis if you can and take a pic.

Edited to add: That is a bias adjustment pot.

[Disturber]

Thanks for the info, great help.

I think that the orange drops are original. Fender used them at the time. They are both in my Super Champ and Deluxe Reverb II from the same era, around 1980-1981.

[crunchee]

Wow! That's a nice example! Does it say what the power rating is on the back panel?

[backinit]

I purchased one of those new back in HS. I ran a DOD 250 through it. Memories..

[Disturber]

Some more pics from the inside:

The back has no info on how many watts this thing puts out. I guess it is 35 to 40 watts.

[stobro]

"TOTAL LOAD 4 OHMS 40 WATTS RMS" right under the speaker jacks!

[Brewmaster]

Those Mallory filter caps are original, looks like from 81. Speaker codes are from 81 so I guess it's an 81.

I can't really read the tranny codes, could be my crappy monitor.

Here is another sites for dating parts. http://home.provide.net/~cfh/pots.html

Make sure those filter caps have no bubbles or leakage, I can't tell from the pic.

One of the last "real" Fenders and a great find.

[Disturber]

"TOTAL LOAD 4 OHMS 40 WATTS RMS" right under the speaker jacks!

Dough! Didn't read that line properly...

There is something not right with the bias. One tube was running at 60 mA. I took the bias down as much as I could, one is now as 20 mA. The other one still is high. Could be that the power tubes are just bad, or the bias circuit needs some tweaking. I won't play the amp until I have tried with fresh tubes. If it's not correcting the problem then I'll leave it to my tech for a check up.

There is a Sovtek 5AR4 in the amp now, I will put in a correct 5U4 GB to get some more sag. And I have ordered a set of TAD 6L6WGC-STR tubes.

How often were Fenders equipped with Rola speakers? How are they quality wise? Sound good at higher volumes?

[Brewmaster]

"TOTAL LOAD 4 OHMS 40 WATTS RMS" right under the speaker jacks!

Dough! Didn't read that line properly...

There is something not right with the bias. One tube was running at 60 mA. I took the bias down as much as I could, one is now as 20 mA. The other one still is high. Could be that the power tubes are just bad, or the bias circuit needs some tweaking. I won't play the amp until I have tried with fresh tubes. If it's not correcting the problem then I'll leave it to my tech for a check up.

There is a Sovtek 5AR4 in the amp now, I will put in a correct 5U4 GB to get some more sag. And I have ordered a set of TAD 6L6WGC-STR tubes.

How often were Fenders equipped with Rola speakers? How are they quality wise? Sound good at higher volumes?

Good choice with the TAD and yes, do try the 5U4 it will lower the voltage as well.

I don't see the wire going from the junction of the 220k resistors to the wiper (middle lug) of the bias pot. I notice a couple of other things different so the amp does not have the standard adjustable bias as found in a BF Fender but instead looks to have the SF bias circuit. It's easy enough to do and any good tech can fix this cheap.

[crunchee]

One of the last "real" Fenders and a great find.

+1! It's cool that it doesn't have the funky power increase that bigger Fender amps had at the time. It looks like a very snag-worthy amp!

I don't see the wire going from the junction of the 220k resistors to the wiper (middle lug) of the bias pot. I notice a couple of other things different so the amp does not have the standard adjustable bias as found in a BF Fender but instead looks to have the SF bias circuit. It's easy enough to do and any good tech can fix this cheap.

I've always wondered about the 'bias balance' circuit...supposedly, Fender changed it to this from the earlier 'bias adjust' circuit, in order to be able to use random unbalanced power tubes...the theory being that you can 'average' setting the bias between two random power tubes (and get away with it), and skip having to match up sets of tubes, reducing time and money otherwise spent in order to match tubes. My question is, if your power tubes are ALREADY balanced (as most paired sets of power tubes seem to be sold as anymore), then does the 'bias balance' control act like a 'bias adjust' control (since the tubes are supposedly equal or close to it already), or does the control really DO anything bias-wise with a equal, matched set of power tubes?

[Disturber]

One of the last "real" Fenders and a great find.

+1! It's cool that it doesn't have the funky power increase that bigger Fender amps had at the time. It looks like a very snag-worthy amp!

I don't see the wire going from the junction of the 220k resistors to the wiper (middle lug) of the bias pot. I notice a couple of other things different so the amp does not have the standard adjustable bias as found in a BF Fender but instead looks to have the SF bias circuit. It's easy enough to do and any good tech can fix this cheap.

I've always wondered about the 'bias balance' circuit...supposedly, Fender changed it to this from the earlier 'bias adjust' circuit, in order to be able to use random unbalanced power tubes...the theory being that you can 'average' setting the bias between two random power tubes (and get away with it), and skip having to match up sets of tubes, reducing time and money otherwise spent in order to match tubes. My question is, if your power tubes are ALREADY balanced (as most paired sets of power tubes seem to be sold as anymore), then does the 'bias balance' control act like a 'bias adjust' control (since the tubes are supposedly equal or close to it already), or does the control really DO anything bias-wise with a equal, matched set of power tubes?

Interesting question. As I am as dumb as a donkey when it comes to poking around the interiour of an amp - but as interested in how it works as a fly to a turd - I hope someone can answer this.

What would be the main benefit of re-building the bias-circuit to BF standard? Compared to leaving it as it is today?

[Brewmaster]

Interesting question. As I am as dumb as a donkey when it comes to poking around the interiour of an amp - but as interested in how it works as a fly to a turd - I hope someone can answer this.

What would be the main benefit of re-building the bias-circuit to BF standard? Compared to leaving it as it is today?

Modding the bias circuit makes the bias fully adjustable. I like this better even if the tubes are 4-6 ma apart.

I hate to say this but some magical even order harmonics can and do happen with tubes that aren't matched and you average the bias point. They didn't match tubes back in the day and its part of the old tone folks are looking for that is never accounted for in "tone recipes". There is a lot of debate on this and a lot of psycho-babble and pissing matches amongst the tech community but the bottom line to me is my ears don't lie.

When your tubes come in try them out and see if they settle in at a decent bias point. If they do don't worry about it, you know what will work from here on out. Copy down the specs of the tubes and order as close to possible as you can.

[Disturber]

I picked up the Vibrolux from my tech today.

He re-built the bias circuit so I can properly adjust bias, and he kept the balance pot - so I guess I can use miss matched tubes if I want as well.

A grid resistor had come loose on the output tube, that is why it was running to hot. He fixed that.

He did some blackfacing to the output stage. He also kept the GZ34 tube, I'll experiment with a 5U4 as well and see what I like best.

Bias set at around 34 mA. New TAD 6L6 tubes.

I just played it the basement tonight at bedroom level but it sounds promising, damn warm and with that great Fendery trebly top chime. Will turn it up to ten over the weekend. I am quite positive that this is amp is a keeper. I'll see if I can do some sound clips.

[Feynman]

Will turn it up to ten over the weekend.

Man - I need to do that once in my life.

[Disturber]

Will turn it up to ten over the weekend.

Man - I need to do that once in my life.

metaphorically speaking. I meant turning it up until I get some true power tube distortion. No master volume, so It has to be done the hard way.