Peavey Delta Blues output question

[Randall]

Disclaimer: I hate working on these. The layout and little jumpers between boards just put me in a bad mood. So there's that.

But what purpose does wiring the filaments of the four EL84's in series like an old school Christmas tree serve? Who else does this? One came in as not working, with three tubes in it. I took it all apart to get to the board BEFORE I looked at the schematic, and THEN found that it needed all four in order for the quad to light up. Don't do that.

And what purpose does having a screen resistor only on one tube of each pair serve? maybe to unbalance and dirty things up?

http://www.freeinfosociety.com/elect...wPmOqks7zD3-sc

[g1]

Someone will be along to straighten us out shortly.

[Leo_Gnardo]

Hardly a straighten-out, I think PV is wacko for their series-filament circuit. Well, maybe not. Sorta forces you to have a somewhat matched output tube set, if only to keep the filaments glowing more or less evenly. Delta Blues, 50 30 & 20W Classics too. The construction method as you can see, is to break apart 3 boards like crackers, then wire them into that "U" shape with a jillion crappy little jumpers. Made to be assembled, not disassembled.

I can understand somewhat, Peavey's series filament string for preamp tubes in their hi gain amps 5150, JSX, XXX, like that. Although it makes it a PIA to troubleshoot those too.

[Enzo]

A too common problem with modern amplifiers is the high current heater distribution. How many times on how many brands/models have we found ribbon cable connectors burnt on the heater feed pins?

PV has been running heaters in series for YEARS. Preamp tubes in particular. 5150 from 1992, Triumph from 1988, others. Those small EL84 amps from 1994 in the Classic 30 and Delta Blues. (Which are the same circuit with a simple trem added.) Those are the earliest power tubes in series on the PV line. The current Valve King has ALL the tubes in series. Well sorta.

In the Classic 30/DB, those four power tubes draw 0.76A heater current, that instead of 3A a parallel would draw. This means a lighter winding on the PT and less potential damage to connections. A more reliable amp.

I am surprised you have not seen this before, those amps have been very popular the last 20 years. But now that you have seen it, you won;t forget it. In fact, for the guys who just HAVE to pull half the power tubes in their amps, someone ran a thread about making a pair of dummy EL84s by snipping off a few of the pins, leaving the heater pins.

Using higher voltage lower current heater power, that PT winding also can do double duty for the low voltage rails most amps have these days for ICs and relays and what not.

Preamp tubes in series are always (as far as I know) run on DC, so that cures some hum situations right there. +/-24v or +/-18v powers 4 or 3 12AX7s in series. Lower current is better for the connections.

When I see an amp, even ones I am familiar with, I generally get out the schematic first, just to look for any reminders or gotchas I can spot.

And what purpose does having a screen resistor only on one tube of each pair serve? maybe to unbalance and dirty things up?

Don't think so deep. First, it doesn't unbalance anything because the push and the pull each have the same thing. Besides, no one designs a mass market amplifier purposely dirty like that. Just think of the amp as not having screen grid resistors. Like the Classic 20. But to prevent the same side tubes from interacting undesirably, they put the 100 ohm between them to decouple them. Peavey was doing that as far back as 1975 on the Deuce.

[Master Po mode]And now the Tao of the Ten Screws[/Master Po mode]
(from a career in another industry, but apropos)

When facing a situation where you have to remove TEN FREAKING SCREWS from something to work on it, there is a choice. One can piss and moan and scream, and then take out the ten screws, or one can just take out the ten screws and get on with life.

I don't like the way the C30/DB is laid out either, but having done it a time or two, I can bop that circuit board out of the chassis in just a few minutes.


What bugs me is a chassis that fits too snug in the cabinet, and when you try to remove it, the chassis or the cage nuts or something snags on the edge of the tolex and rips it up. Marshalls and Fenders there a lot.

[Enzo]

In all my decades, I very rarely see open heaters in tubes. But to troubleshoot a string of them? Ther is a supply at one end, you will see it down to the point of the break - whether tube heater itself or connections -

[Randall]

I don't think anyone is bitching about ten screws. I think it's about having to bend these things open and closed on their hard jumpers whenever one needs to get inside to do something, and the potential future problems that creates.

[Enzo]

And I was not thinking of you specifically either. But the average complaint is how complicated it is to get it all apart.

My tao is not about screws necessarily, but about some task perceived as overly complex.

[Randall]

I have been bitten in the ass so hard with one of these in the past because of that hard jumper stupidity that I am "negatively biased' towards them. It IS difficult when one gets to a certain point with these.

[Enzo]

Oh and wait until you try to fire it up with the board out of the chassis, and you find you have to use all the jumper clip wires you have to complete all the grounds.