Wreckit 2xEL84 build

[Smokebreak]

I'm starting a build to emulate the sounds coming from a Zwreck. I'll run 2xEL84 with a 270-0-270 PT and a 6.6K Deluxe type OT, because that's what I have on hand. Therefore this is not a clone.
I'm referencing AC30TB preamp, with lower filtering, and running the B+ string droppers off the screen node, ala early Vox( I've seen this called "Parallel" droppers, but I'm not sure why, as the resistors only share the same point at 1 end?) , as well as implementing the known differences between the Zwreck and the AC30. I'll be referencing the Rocket too!

I've made adjustments to the Rocket and AC30 schematics(the base of which I found here on this forum) for only 2 El84s, and would appreciate thoughts/concerns/suggestions.

I'll leave out the standby switch with the GZ34, and will probably put the CF resistor to ground on a switch. I imagine I'll play the PI plate caps by ear, as well as the Rk for the power tubes : [img868]http://www.whiteghostshivers.com/images ... reckit.png[/img]http://www.whiteghostshivers.com/images ... reckit.png

[Blackburn]

I wouldn't put much thought into coupling cap values. Sticking with the .022uf and .047uf caps with the first coupling cap as 500pf would be my advice. You may want to add a choke after the GZ34. Something in the neighborhood of 15 - 20 henries should be fine. And you'll probably find that 100R is too low for your cathode resistor. You're gonna be biased pretty damn hot! Looks like you got much of the Z Wreck figured out, though. Looking forward to seeing this build.

[Smokebreak]

Ok thanks. I just put in a Mouser order and splurged on a few of the chassis mount aluminum resistors. I think I got 100,120,150 in 10W so hopefully I'm covered. As I'm sure you know, living in Texas, mouser takes about 30 hours from order to delivery. Love it! If only they had cheap electrolytics..
As for the choke, I've never used one in a build(cheap), so I'll give it a go. I found a choke i have from an organ pull that is from a Hammond AO43, CH301 on the schematics, and looking at the schematics, it's 14H and was in the Reverb section. Do you think it will work? Here it is, left side of the reverb and power amp section, which is top right: Looks like its seeing 285V, and has around 500ohms resistance measured, http://www.captain-foldback.com/Hammond ... _early.gif

I'm not sure how to determine if it can handle the current in the PS.
Also, I'm assuming I would put it between the 1st and second B+ nodes? (that is where I substituted the 2K2 for choke in the first place) ...just making sure.

[Blackburn]

I had a look at that schem and it seems to have a dual EL84 power section, so I'd say you should have zero issues using that choke, especially since the organ has more more current draw with all the extra novals in there compared to what you're building. Also cool using old iron for that extra mojo. And yes, you wire the choke off of the rect between the first two filter caps. I'm glad you chose not to use a standby. I didn't use one either.

I hate standby switches, unless I need them.

[Smokebreak]

Right on. Here's a great read for those interested on the use of standby switches, especially concerning GZ34. Dig the light bulb analogy.
http://charliehall.proboards.com/index. ... thread=958

[JazzGuitarGimp]

Right on. Here's a great read for those interested on the use of standby switches, especially concerning GZ34. Dig the light bulb analogy.
http://charliehall.proboards.com/index. ... thread=958

All of this makes good sense. Merlin, in his books, talks about how there is no harm to [receiving] tubes in equipment that does not have a standby switch. Transmitting tubes are apparently another story (something to do with cathode depletion IIRC). It would be simple enough to fit a "mute" switch where you normally have a standby switch. Then you have the convenience of no noise from the amp while on break - or the uncool event of a drunken patron deciding to take your guitar for a spin while you're away...

[xtian]

If only they had cheap electrolytics.

They do, but they're radial lead. I bought 22uF and 33uF 450v radial from Mouser, and found tidy ways to use them on turret boards without standing them on end.

Here you go:

http://www.mouser.com/Passive-Component ... ricing%7C0

[Smokebreak]

They do, but they're radial lead. I bought 22uF and 33uF 450v radial from Mouser, and found tidy ways to use them on turret boards without standing them on end.

Here you go:

http://www.mouser.com/Passive-Component ... ricing%7C0

Oh man that is GREAT! Thanks a bunch. I guess I always looked for axial and they have those but they're designer-ish, so I assumed the radials were the same.

All of this makes good sense. Merlin, in his books, talks about how there is no harm to [receiving] tubes in equipment that does not have a standby switch. Transmitting tubes are apparently another story (something to do with cathode depletion IIRC). It would be simple enough to fit a "mute" switch where you normally have a standby switch. Then you have the convenience of no noise from the amp while on break - or the uncool event of a drunken patron deciding to take your guitar for a spin while you're away...

...and you would think major manufacturers, in the pursuit of saving $$, would be keen to this, as good switches aren't cheap, as far as the little components go..

[martin manning]

Right on. Here's a great read for those interested on the use of standby switches, especially concerning GZ34. Dig the light bulb analogy.
http://charliehall.proboards.com/index. ... thread=958

I don't think I'd call this a great read, nor even good... This statement seems particularly confused: "Note, for the sake of this argument, I am only discussing amps that use a GZ34 rectifier tube or the Weber replacement. So JTM45, AC30, Bassman, etc. Amps with other tube rectifier types or solid state rectifiers are not part of this discussion." Why only GZ34? Any rectifier, SS or vacuum, would suffer a high-current surge in the configuration where the standby is between the rectifier and the reservoir. That, along with a GZ34, is exactly what the 5F6-A Bassman has.

Much better information is available here: http://www.valvewizard.co.uk/standby.html

[Blackburn]

The ValveWizard's is a very informative read. One of my favorites. I do wonder about placement of the choke that he mentions, since I've seen a few reputable builders do exactly what he advises against. One example is the Mazerati GT by Z. When I owned mine, I peeked inside and he had the GZ34 standby reservoir choke. I simply didn't use the standby when I had it. I'm curious about this.

[Bob S]

I need to re-read Merlin's bible on this.
I seem to remember him stating that a standby switch is unnecessary.
Personally I'm nervous about using more than a 64uF reservoir with a GZ34.
Certainly when there isn't a standby switch.
Ken used 80uF on the Rocket, with a standby & choke.
When I see the price of old Mullard GZ34's it makes me a lot more careful.

[martin manning]

The ValveWizard's is a very informative read. One of my favorites. I do wonder about placement of the choke that he mentions, since I've seen a few reputable builders do exactly what he advises against. One example is the Mazerati GT by Z. When I owned mine, I peeked inside and he had the GZ34 standby reservoir choke. I simply didn't use the standby when I had it. I'm curious about this.

I don't like that arrangement since the rectifier gets a high-current surge when the standby is flipped. Merlin says the worst place to put a standby switch is right before the choke in a capacitor input PS due to the flyback voltage that develops when the switch is opened. That's rectifier -> reservoir -> standby -> choke. Well, that's where Fender has put it since the Blond era, and it seems to hold up fine. The vacuum rectifier gets a slow start that way. I do think it's best if the main power is turned off a few seconds before the standby, though, which avoids the voltage spike and lets the reservoir drain along with the other filters.

[Blackburn]

I imagine there can be an issue at some point with that setup, but for the most part, I don't think it's as bad as theorized. My tube rectified builds don't get standbys and my SS rectified builds don't get chokes, so there's really no issue for me. When using a SS, I like keeping the reservoir on the hot side of the standby with bleeders. Works for me and it's quiet when switching.

[cbass]

Could a NTC Thermistor be Useful somehow?When running a largeish cap with a tube rectifier.

[rooster]

First off the circuit DOES have a choke - in the form a the 2K/3W resistor that attaches to the OT center tap. And make this bigger probably, 10 Watt sand block is much better but you decide. Ken uses 25 Watt 'chokes' in his builds.

As to Merlin and the standy before the choke using a rectifier tube, as Martin says Fender has created a long running example with no issues. But here in this case Fender uses a .05/600VDC poly cap to ground - something missing from the schematic you show. So consider this if you build this circuit. I for one have purchased a Merlin book or two and, frankly, found it to be so 'lofty' in practical terms that it is virtually worthless to someone building guitar amps. Ha! I really do. The history is there, the Bassman circuit is sound.