10/12/2023 0 Comments Fender musicmaster bass amp mods![]() I doubt the transformer was designed to handle the DC or the bass well, the whole circuit was designed to be economical in a day when decent capacitors were a new emerging innovation.Īnd heck it's not even arrived yet! I'm just enthusiastic. So to me it's an interesting experiment, and I appreciate the conversation. ![]() There actually are even some advantages to having that variable DC on the primary instead of just variable AC, because the typical single-ended transformer doesn't experience the nonlinearity of the magnetic hysteresis of the metal which occurs when the magnetism changes direction. Admittedly a transformer design optimized for the redesign might work much better with capacitor coupling! I really would like to take one of these transformers apart to inspect the core it's quite possible there is no air gap and the power is so low it just handles the DC. But I've stumbled onto an attractive topology, using capacitor coupling to an interstage transformer! Now suitable caps are more readily available or they probably would have done it back then! Even now, even with a transformer with a gap, adding 1 coupling cap and one plate resistor might improve the transformer performance. And I've always liked single-ended outputs that are capacitor-coupled instead of the DC on the transformer, but at high power there are always major disadvantages. I'm really into the interstage transformer PI instead of more tube stages. This is a DIY site, and people like me will try stupid things you would not. This is a cheap toy to learn on, and hopefully enjoy afterward. This is not warranty repair, nor is it seme revered vintage treasure. I'm just trying to understand the circuit, and experiment a bit to learn something, and have some fun. I suspect it's probably there for a multitude of reasons, damping any ringing resonances of the circuit, maybe also to carry some of the DC for the plate so the transformer core doesn't saturate, perhaps some accommodation of the available transformer.Įnzo, I'm not determined to get rid of that parallel resistor. The only thing i really not sure of (thinking about it now) is whether or not the the schematic had 6V6s or if it was the 6BQ5(EL84) version.Īll the ones I found online that with the mains drawn the way Im describing have 6BQ5s, and the amp I was working on had 6V6s.Yes, a lot of people online have eliminated the resistor and experienced a loss of treble. But Im pretty sure I remember it looking like original Fender. Is it possible you're working drom the "unofficial" schematic? And thatcthe creator's example had one of those batshit bare wire fuses but it was mistaken for a piece of wire? The single Fender layout diagram I found did not show anything either. But a third "unofficial" schematic seemed common that was NOT official Fender, that did not show anything. I found two official Fender schematics one of which showed a "CSA Thermal Protector" & the other which showed a regular fuse. ![]() But they also look a good bit different from any official Fender schem I've seen, compared to others of thecsame period. Have any of you run into this on this model?ĥ4144Now that's cheap and dangerous of the bean counter.Įdit: seems all of the "homenade" schematics show 6AQ5s. The mains current didn't exceed much more than ≈500mA at full output, so I chose a value of 1A/slow. The cap was removed, and installed an inline cap from the live to the power switch.īefore choosing a value, I ran the amp into clipping at full power, while monitoring the mains current draw. Inside, there was the typical 70's fender tag strip with one of the legs of the incoming mains coupled to the chassis with the blue radial cap. Apparently, fender installed what appears to be a thermal fuse in some other/later models. It has a UL sticker on the back panel as well. I double checked on the schematic and confirmed that it was designed and built without one, which is crazy to me. ![]() I mean, there was no mains fuse at all, and there never was in this amp!!. Not like, the fuse was missing from the fuse holder. So, after replacing the mains power cord with a new molded plug, I went to check the fuse and. One of the other routine checks I make, particularly in vintage amps, is confirming the fuse value and rating is the one specified. More often than not, it's a disaster and it gets replaced–as this one did. We see this a lot, and I always check the condition and wiring inside. The molded plug end had been replaced by an old 3-prong replacement with screw terminals. We had a 70's Musicmaster Bass amp that came in for general cleaning/service (dates to '79, it looks like).
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