Wreckit 2xEL84 build

[Smokebreak]

I revisited my Zwreck build last night after the honeymoon and have decided there is just wayy too much bass and mids in my build. I've gone over my wiring and values 5 times, and inquired about the seeming backwards wiring of the bass pot here http://ampgarage.com/forum/viewtopic.php?t=21671

The amp just sounds congested, and falls apart somewhat when overdriven. It's like there is no sweet spot.

I'm using a 540CT PT, though I'm reading 565VAC across the plates of GZ34 loaded. My schematic is at the beginning of this thread, and in the PS I'm using the parallel dropping string off screen node of 27K/22K/27K. With this setup, compared to the Rocket voltage chart, I am nowhere close, as my first stage is 145Va(50% high), CF = 185/255(40% high), PI =236/238(30%), el84=340(20% high). This makes me think that despite their similarities, the Zwreck will perform quite differently from the Rocket.

Can anyone that has built one of these confirm these voltages or comment on the dropping string values, or offer any other insight?

I did find that dropping the first 2 cathode caps to 1uf and 2uf is getting me closer , and dropping the first stage plate resistor to 100k helps keep things together. Now it sounds more like a silverface vox somehow, which is pretty neat sounding, but obviously a different animal.

Any input is appreciated.
Jeremy

[M Fowler]

The dropping string is not as simple as the Rocket.

You need to use a PT with 560vct or less HT is even better sounding.

Mark

[M Fowler]

Here are three photos of my amps.

Two are combos (Rocketeer) and one is a clone Zwreck head version (wreck).

Mark

[Smokebreak]

The dropping string is not as simple as the Rocket.

You need to use a PT with 560vct or less HT is even better sounding.

Mark

Thanks Mark, for the pics as well. My PT is 540CT and I'm confident my dropping string is wired correctly. It's the values I'm unsure of, as well as the interaction and voltage results, as opposed to a standard series dropping string .
Mine goes 27K/22K/27K, all off the screen node, as I have seen suggested, and with these values voltages are quite different than th Rocket... Which is fine, but I have also seen suggested that preamp voltages should be the same as Rocket.
It looks like your string is 27K/22K/20K? Wouldn't that mean your V1 would be even higher than mine?
I'll fiddle with the string, but have a feeling this will turn into a Rocket by days end...

[M Fowler]

I don't know what the voltages are compared to a Rocket.

I don't seem to have my voltage charts though I sure remember adjusting V1 and V2 to get closer to Rocket voltages. Maybe some one with a real Zwreck will tell us the voltages.

Mark

[Smokebreak]

Alright, Well I just wired the B+ string like the Rocket, in series. My B+1 is 350. Other than that, I've adjusted dropping resistors so that all other plates except for el84s are on par with current voltage chart. I have 2 questions:

1 . Assuming I'm not going to get into lowering my VDC at the rectifier, what are the effects of having all voltages "on spec" , versus having all voltages on spec EXCEPT for el84 plates, being 50V higher than spec?

2. This one has me baffled. Right now I'm running 27K/10K/10K in the series dropping string. Obviously the high value of 27K (instead of 18.2K)is to reduce B+ from the PI on down. I'm trying to get my V1 plates up a hair, but no matter much I reduce the last 10k feeding the node to V1, I cannot get my plate above 87V. I have even connected B+ from the CF node directly to v1 plate resistor/cap, with the same result. The only way I can get the plate up is to decrease the plate resistor. How is this possible?

[martin manning]

You mean the V1 plate, since there is just one triode in use, right? What are the voltages on the plate, grid and cathode of that triode (pins 1, 2, and 3), and what is the concurrent voltage on the other side of the 220k plate load?

[M Fowler]

Zwreck dropping string is not wired like a TW Rocket.

B+5 feeds from B+2 cap
B+4 feeds from B+2 cap
V2 orange wire to B+4 cap

Mark

[Smokebreak]

You mean the V1 plate, since there is just one triode in use, right?

Correct

What are the voltages on the plate, grid and cathode of that triode (pins 1, 2, and 3), and what is the concurrent voltage on the other side of the 220k plate load?

100V plate, 0V grid, .83V cathode. On the other side of the plate load is 223V, and B+4 is 226.
Since my last post I have gone to strict Rocket specs series dropping string(18.2/9.1/9.1) which is not drastically different than what I had in my previous post, but my theory question still applies: if the dropper to V1 drops only 3 volts, why even bother with it and why not just feed it the voltage from the previous node? Is the dropper for V1 just there to decouple it from the previous node and add an extra filtering stage?

Zwreck dropping string is not wired like a TW Rocket.

B+5 feeds from B+2 cap
B+4 feeds from B+2 cap
V2 orange wire to B+4 cap

Mark

Yes this is exactly how I wired it originally. In my pics your orange wire is my grey wire. Since then, I've wired the dropping string at least 5 different ways... Series/parallel/rocket/Zwreck/trying to gett all voltages proportionally higher than Rocket specs based on my PT/trying to get all preamp specs dead on with Rocket specs with only higher voltage on EL84s, etc....
I've found the only significant difference between Rocket and Zwreck are the voltages applied, and their proportions to one another in each circuit.
So, I'm just tring to make sure I've got the values of the dropping string correct for the Zwreck (27K/22/27 ?)before I dismiss it and move on, as I'm not a huge fan, the way I originally wired it with that string. Hell I'm already into Rocket territory and it's dropping string provides a lot more smoothness in breakup.

[martin manning]

You mean the V1 plate, since there is just one triode in use, right?

Correct

What are the voltages on the plate, grid and cathode of that triode (pins 1, 2, and 3), and what is the concurrent voltage on the other side of the 220k plate load?

100V plate, 0V grid, .83V cathode. On the other side of the plate load is 223V, and B+4 is 226.
Since my last post I have gone to strict Rocket specs series dropping string(18.2/9.1/9.1) which is not drastically different than what I had in my previous post, but my theory question still applies: if the dropper to V1 drops only 3 volts, why even bother with it and why not just feed it the voltage from the previous node? Is the dropper for V1 just there to decouple it from the previous node and add an extra filtering stage?

Those voltages seem to check out, and yes decoupling is the primary purpose of the last RC filter.

[Smokebreak]

I cracked back open this amp today after watching that Queen in Montreal(?) concert again, as May's tone just gets me giddy. After many failed attempts to emulate that sound with this 2xel84 zwreck/rocket/ac30, I chalked it up to not having a treble booster, or 9 AC30s. So when reality hit, I just changed the tonestack to Fender, and this is as happy as I've ever been with this amp(sounds nothing like May btw). The Vox stack was just way too middy and boomy and just kinda a mess to my ears when cranked. I kept the 500K pots in but may cheat in 250's, with 5K2 mid resistor. Much more focused now, and still chimey. Parallel dropping string 22K/10K/27K.

[wsaraceni]

interesting thread i'm going to have to recheck my voltages as this is essentially what i built but i had a ez81 rectifier and marshall 18 watt transformers