Fender Musicmaster Bass amp - 6AQ5 version

[Bob M.]

Hi,

I've acquired a chassis for a Musicmaster Bass amp. It has a few things still present in the chassis. One of them is the pilot light which is different than the typical Fender 6.3 volt bulb and holder (and jeweled pilot lens). It's one of the changes made by Fender between the 6AQ5 version and the 6V6 version of this amp model, as they returned to the more typical pilot light set up when they updated this amp model to 6V6 power tubes.

My question: how is this pilot light for the 6AQ5 version wired? I don't want to ruin the part by trial and error so I though I'd ask once (or twice) and cut once. I can't seem to find a schematic online for the 6AQ5 version of the Musicmaster Bass.

Thanks in advance for your on-point answers,

Bob M.

[olddawg]

Hi,

I've acquired a chassis for a Musicmaster Bass amp. It has a few things still present in the chassis. One of them is the pilot light which is different than the typical Fender 6.3 volt bulb and holder (and jeweled pilot lens). It's one of the changes made by Fender between the 6AQ5 version and the 6V6 version of this amp model, as they returned to the more typical pilot light set up when they updated this amp model to 6V6 power tubes.

My question: how is this pilot light for the 6AQ5 version wired? I don't want to ruin the part by trial and error so I though I'd ask once (or twice) and cut once. I can't seem to find a schematic online for the 6AQ5 version of the Musicmaster Bass.

Thanks in advance for your on-point answers,


Bob M.

What does it have? A neon lamp off of the mains. An LED? What voltage supply does it use. How much of the amp is left? If it's gutted you can use the iron and chassis to build whatever you want wit that tube compliment. Are you sure someone didn't replace the 6.3 v lamp and use a different supply for the lamp to free up more heater current for another tube or something?

[Enzo]

Interior photos would sure help answer your questions.

But without that, why would the type of output tube matter at all to the pilot lamp?

[nickb]

Hi,

I've acquired a chassis for a Musicmaster Bass amp. It has a few things still present in the chassis. One of them is the pilot light which is different than the typical Fender 6.3 volt bulb and holder (and jeweled pilot lens). It's one of the changes made by Fender between the 6AQ5 version and the 6V6 version of this amp model, as they returned to the more typical pilot light set up when they updated this amp model to 6V6 power tubes.

My question: how is this pilot light for the 6AQ5 version wired? I don't want to ruin the part by trial and error so I though I'd ask once (or twice) and cut once. I can't seem to find a schematic online for the 6AQ5 version of the Musicmaster Bass.

Thanks in advance for your on-point answers,

Bob M.

I have one of these on my bench right now. I'll take a couple of gut shots tomorrow and repost when I have them. If there is anything else you need to know, now is the time to ask before I close it up again.

Edit: Added pics - lots of overlap!. Note this is the 240V version. The indicator lamp is a neon wired between neutral and the 120V tap on the power transformer, in this case. Note there is no fuse or thermal limiter in this model. That is something that needs to be addressed.



IMHO, although it seems this amp was built to the lowest possible price point and is quite unsuitable for bass, it does breakup in a rather rather unique and nice way.

[Bob M.]

Ok guys, thanks for the replies.

I've actually found a schematic deep in my Fender files for 1st version of the Fender Musicmaster Bass amp. Sorry for the now erroneous post; I didn't know I had this schematic and I hadn't looked at it in years. It appears that the pilot light is a neon device wired across the AC primary (from hot to neutral), as NickB said. Before I knew that, I didn't want to destroy this device by trial and error experimentation as it would be near impossible to replace and why not keep the amp original, if possible.

Here's a little Musicmaster Bass amp history. There are two and possibly three versions of the Musicmaster Bass amp. Version #1 uses 6AQ5 power tubes, has the aforementioned neon lamp pilot light and the on / off switch is combined with the volume control, like a 50s TV set. Version #2 has the traditional 6.3 volt light bulb, holder and jeweled lens, as I mentioned. It has 2 x 6V6 power tubes and has a slide switch very similar to a Fender blackface/silverface style bright switch for the on/off function. These are the identifying characteristics so one can tell which version he is dealing with, especially by looking at just a photo. This is the only reason I mentioned the power tube compliment - to distinguish the various versions from one another. I've heard there is a 3rd version (but never seen one) - a blackface Riviera era version but I have no idea what to expect to find inside one of those amps.

This is the only Fender amp I've seen that does not have fuse protection of any sort. There is no external fuse holder, there is no internal fuse, as Nick B. has pointed out. In this situation, I usually use an inline fuse holder as one might see in a car radio installation and add this to the circuit AC primary. But there are other ways to realize fuse protection, of course. It's amazing that this amp has a UL seal on the back panel!

I'll build something cool inside this amp. For now, I haven't decided. Maybe a Z-28 type circuit using an EF86, 2x 6V6 power tubes, etc, etc. Don't really know yet. There is no iron currently in this amp so I get to choose. I don't know what has happened to this amp since manufacture but I can say two things, unequivocally: The pilot light is dead stock and the chassis is unmodified (no extra holes). I've seen (and owned) a number of these silverface Musicmaster Bass amps over the years. They used to be a good buy years ago but like anything that says Fender on it, they have skyrocketed in price, regardless of the quality of the inside circuitry. Enough people like them to keep this going.

Anyway, Thanks for your replies (thanks, Nick) and I'm sorry it turned out that I actually had the schematic,

Bob M.

[nickb]

Glad you found it

I'd appreciate it if you could share the 6AQ5 schemo, please. I did a part by part check on the one here against the 6V6 schematic and I believe it is the same, aside from the protection and indicator already mentioned. But, it's would be nice to see, just in case.

Here she is sporting a new front and hanging out with some buddies.

[Bob M.]

Hi NickB,

Unfortunately, I don't have access to a scanner so I don't know how to get the hard copy schematic into my computer (I'm kind of a computer-dunce). I'm happy to (snail) mail you a copy once I go to the Xerox copy place. In the interim, I'm happy to answer any questions you have about this schematic. As I've owned both versions #1 and #2, I'm pretty sure that the circuits are exact to one another besides the 3 things I mentioned in my above post (pilot light, power tubes, on/off switch) and of course, the version #2 silverface fascia panel itself does not say 'on/off' on it, nor does it have the numbers printed around the control pots because the #2 version used traditional Fender knobs of the era (which have the numbers printed on them). So the front silverface panels are cosmetically different from versions #1 and #2 (this is also true for the blackface #3 version). I don't buy these anymore but if I did, I would only consider the #2 (6V6) version.

Looks like you've got some nice amps!

Bob M.

[nickb]

OK. No need to go to all that trouble - but thanks just the same. Confirmation that they are basically the same is all I really needed.

[52 Bill]

OK. No need to go to all that trouble - but thanks just the same. Confirmation that they are basically the same is all I really needed.

There is a pdf copy at the Ampwares site. It is the same circuit but with 6AQ5 tubes and a neon indicator.

[nickb]

Thank you, Bill.

[Bob M.]

This schematic, graciously provided by 52 Bill, is exactly what I have here (as a hard copy). The only thing I would add is that my schematic also says '126771' which is the Fender part number for the schematic drawing.

On the faceplate, on the lower left, this Musicmaster Bass amp says ' Model CFA7010'. I'm wondering if this model code has any significance? I've noticed a similar model code on many 70s silverface Fender amps that came and went a short time after. I guess it was some sort of CBS attempt at organizing the chaos at Fullerton. Maybe CBS sent in some east coast efficiency expert saying you must have a model code besides the amp name, who knows?

Bob M.

[nickb]

Mine says CFA7010X on the faceplate. I'm guessing "X" for export?

[Bob M.]

NickB,

I went over version #1 and version #2 of the Musicmaster Bass amp schematics very carefully and they are exact to one another. The marked voltages on the Version #1 schematic are down by about 2 volts from version #2 but's that pretty insignificant as the transformers, rectifier diodes, filter caps and resistors are all the same on both versions. The Version #2 (6V6 tubes) has a CSA thermal protector, Fender part # 101872 and the version #1 amp does not (at least on the schematic). I think we beat this horse to death.

Bob M.