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Discussion in 'The Workbench' started by el_bastardo, Mar 30, 2018.
12BZ7 has a mu of 100, like the 12AX7 but it has twice the transconductance so it is a much nicer tube than the 12AX7. This means that the 12BZ7 is a more sensitive tube (input vs output) than the 12AX7. Stick with 12AX7s... So I can have all of the 12BZ7s! LOL!
It seems that all the vintage amps . . . . even the wrecked ones, are going for steep prices these days. That is a bit high. $500 might not be too bad if all the original iron is in place and unharmed.
But a Twin Reverb in good working order into decent speakers is one of my all time fave tones. Some of them (just like the Marshall amps) can get a decent singing lead tone at somewhat tame volume with a good midrange enhanced boost pedal up front. Then some of them are just loud and then louder.
But a Deluxe Reverb build I think you will really enjoy and it will become one of your favorite amps to play for sure.
On another topic, I made a clip of my Jubilee 2555 Clone to show a member here the changes in it. It now sounds much closer to its cousin, the 2203, that I think you would even like this Jubilee now.
I like Jubilees when other people play them. I just have no use for one for me. I don't go for that kind of tone for my own needs.
The Deluxe Reverb is pretty much the perfect amp for what I need for "Fender sound". It will be primarily a studio amp only. It's very unlikely I'll gig with it. But I'd really like to have that natural Fender amp sound in the studio instead of finagling a Marshall to sound that way and using reverb plug-ins in post. I want it all real all the time.
Depending on how my current donor SS chassis and cab dimensions measure out, I maybe have found a bare bones kit to put into it. I just need to dig that old combo out of the garage.
1. It's blatantly obvious that the socket on the left is not a 12AX7. It could be the previously mentioned power tube, or it could be wired for an EF86 or similar pentode (more likely not an EF86 in this case, but uses the same heater wiring so I mentioned it).
2. Whomever did this did it wrong. Mounting screws are for mounting. Only. Grounded components should go to dedicated ground points that serve no other purpose. Why? For example, if a mounting bolt becomes loose, then the ground becomes loose. Oops.
3. Elevated heaters (for anybody reading this topic that doesn't know) are elevated electronically, not physically. For example, This is often done by connecting the PT heater center tap to the power tube cathodes on a cathode biased amp.
4. Somebody questioned different use of heater wires and the necessity of the twists. The purpose of the twists is to keep the wires consistently, tightly, close together to cancel the hum. This can also be accomplished by 2 conductor (but insulated separately) wire, such as a power cord you might see on a lamp, or even good quality 2 conductor (non-shielded) speaker cable. The cable insulation keeps the wire perfectly, symmetrically together and can be just as good (and sometimes better) than twisting cables.
my 2 cents
i have a marshall 100 jmp clone here that i did not originally build. i bought it as a basketcase.
the chassis did not have enough room to wire heaters as normal for marshalls ( the pre amp tubes were too close to the sides), so i just elevated them and ( re) built the amp as a normal old blackface fender would be built.
i used tight turns in the heater wires and made lovely tallish arches ( nice high chassis ) above the pre and PI tubes below.
When on with volumes up and no playing, its real quiet, better than some factory amps I have here.
Running them high has some obvious advantages as any grid wires etc are nowhere near them, no need to make sure of your 90 degree crossover angles or anything for grid wires.
i know that this is a thread about elevated heater wiring, you've interestingly used the word ' floating' in your original post.
Floating AC heaters for less ground noise is a hi fi trick, ive used it guitar amps and it's clever and amazing and it works.
a lot more info on google.
some info here under ' heater elevation'
Josh, You assume too much. I use locktite on all my mechanical connections, including the Kepps nuts, nothing "comes loose".
I have always considered ground, well ground. How you connect to it differs for various reasons. I have seen ground wire/strap terminate at mounting bolts on all sorts of equipment. A bolt is a bolt and as long as it is secure it makes no difference.
I like my heaters at the bottom because of physics or something like that. Heat rises.
this is an interesting comment, both marshalls and fender are wired like this, with the heaters apparently 'at the bottom' ( at the bottom of the amp, not closest to the surface of the planet)
In fact when viewed in terms of top and bottom, they're wired at the 'top'(closest to the sky, when using the component board as a common reference point).
heat rises as mickeydog5 stated, this is rather bad news for classic fender amps those 6l6's and 12ax7's ( and that power transformer ) pump heat straight into the chassis to cook paper component boards, caps and resistors.
Like grid wires, amp builders are supposed to hug the heaters to ground so ground can do its job better.
I'm reading a lot of ' supposed to' on these forums and not enough ' i built it and it works real good', or 'i bias it where i like it where it sounds best' or ' it sounds better to me this way or that way'.
I do things cause mama said.
You're not the only person reading this thread, and my response is a general concept. That said, see below...
It wouldn't make as much of a difference if everything stayed where it was supposed to. Transformers vibrate and can get hot. When you add things like heat, vibration, and insertion and removal of things like tubes, bolts can come loose. Even with loctite. Is it guaranteed to happen? Obviously not, but why take the risk when you can build the most reliable possible thing with only minimal extra work?
I always have a habit of checking things and tightening but from your points dedicated/seperate connection point(s) would be a good habit.
It can make quite a difference.
The more "gain," the more noticeable the filament noise becomes.
Lower settings will not be the major problem, it happens when you punch it wide open.
When the filament is wired vertically, and the audio is wired horizontally, there is quite a difference in filament noise.
The Marshall layout is probably one of the noisiest concerning filament buzzing. Which is also why DC filaments became the norm in later PCB amps.
The vertical filament wires design comes from Fender amps...