Besides flat tone, you don't want tube shorting out. Seems that their QC has lapsed dramatically and the failure rate has skyrocketed.
If you've got some good 6L6s, try those to see if you get an improvement.
I know, I know....
But Darin, Eurotubes is only a 15 minute drive, or 1 day shipping. It's hard to beat when you want it NOW, got to have it NOW, type of thing. Plus, I was thinking that if I can tweak this amp into some good tone with JJ's, then I should have a decent amp.
I haven't tried KT66's yet, but I had plenty of sparkle with JJ EL34's. My build used a SS rectifier and fixed bias so I'm sure that contributes to more headroom. Don't know about the Sozo's, never tried them. I think I used a combination of Mallory 150s and Sprague PS6s.
I looked over your layout pretty carefully and couldn't spot any errors. I'll take another look at your photos as well, but I suspect you'll find the culprit before I do.
briane wrote:... it really is a journey, and you just can't farm out the battle wounds.
soma_hero wrote:... How close together are your output sockets? I think KT66 needs more room from center to center for heat dissipation. If RJ cut the chassis though i'm sure it's adequate since he's done these before..
Soma,
Funny thing (sorta), I got a panicked note from Rawnster saying he was afraid he had soiled his new chassis because he had just read the tube spacing specs on the KT-66s. I didn't punch the holes for this particular chassis but in a round about fashion I provided the specs for Ron on the tube spacing. He had followed my original Rockster post where I used an Express chassis for the build. So in case I haven't said it before, "Don't do that". I eventually changed the hole spacing on the Rockster chassis and would agree that more is better for the tube spacing on this amp.
Taking a historical look at my own build and considering that heat is the issue that you want to address, everything has worked very well and I've got no indications that a chassis stretcher is needed. If you've ever seen a 100 Watt Marshall with KT-66's (Jimi Hendrix), they could use a little more breathing room (same problem but even more tubes), but generally this wasn't anything that caused problems. Also, the Wreck design also has an open back with a lot more fresh air available. There may be some risk of reducing the extended life of a pair of KT-66's when you get them in close, but it's by no means a disaster.
For anybody considering a KT-66 build, despite the history and varied reasons why it probably doesn't matter, go ahead and put a little more space between those tubes... although you may have to ask yourself, is that part of the Wreck mojo? They are all a little tight on tube spacing.
rj
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Normster wrote:I haven't tried KT66's yet, but I had plenty of sparkle with JJ EL34's. My build used a SS rectifier and fixed bias so I'm sure that contributes to more headroom. Don't know about the Sozo's, never tried them. I think I used a combination of Mallory 150s and Sprague PS6s.
I looked over your layout pretty carefully and couldn't spot any errors. I'll take another look at your photos as well, but I suspect you'll find the culprit before I do.
Hey Norm, thanks for looking. I spent a lot of time with the amp tonight, tweaking to my heart's content. Unfortunately I made no headroom...no pun intended.
I tried the mods to the reverb circuit but it didn't help. The 27k resistor off the b+ to the reverb tranny brought the voltage down, but it didn't increase the reverb volume. I added a .1uf cap to the junction point of the b+ and resistor, but that didn't boost the signal either. grrrrrr
On another note, the amp has almost no headroom. I clipped a 200k R accross the first plate on V1 to reduce the plate to about 109k. That helped a tiny bit in cleaning up the tone. But still, I can turn the amp way down and still hear some hair on the notes. grrrrr
I'll keep tinkering with it, and I'll keep telling myself how much fun this is...better than a great day at work.
I simply can't get any punch or vibrancy out of the amp. Very weird, indeed. Jeez, my express build sounds like fender pro reverb next to this thing.
I pulled the 200 ohm bias resistor, and replaced it with a 250 ohm. Lowered the bias, a good thing for it was a little too hot.
I tinkered around with the lift control. I had a 470k resistor in the lift control to eliminate popping when the lift was engaged. However, with a keen eye from Darin (dartanion), that stupid resistor was completely grounding the lift no matter if I engaged it or not. Also, the value of this resistor skewed the mid tone WAY out of spec. Anyway, I removed the resistor and WOW. I have the amp tone that's in my head! The overdriven crap is gone. It's lean and mean with loads of chime. It sounds pretty much like my Rocket build, but with a little more butt. WOW. You ask why in the world would I have put that resistor in there to begin with? Well, I was advised to do so from a very good and published source. Oh well, even the famous can get it wrong occasionally. Valuable lesson learned here.
One issue remains, the Reverb circuit is still dead. So, more tinkering to do. Even so, it feels great to get the amp up and running and sounding the way I had hoped it would sound.
Now you know one way to get fuzz tone... you can add that to your book when you publish "99 ways to hotrod your amp".
All joking aside, very good work... that is the cool thing about this forum. If you can allow yourself to post up your build pictures and info, then you have some of the very best help there is. Seems you were 99.9% of the way there on your own and just needed some keen eyes to see that resistor issue... I missed it myself. When I get a minute I'm going to look for that reverb problem. I really want that one solved because I think reverb could be the ultimate addition to a Rockster amp.
BTW - It's good to see Normster joining this thread. His talk of a 6V6 Rocket inspired me in building the original Rockster amp.
I liked the comment about the similarities to the Rocket amp. I found the KT-66's to be like giant EL-84's... great stuff and just a little bit more of everything. I haven't read a bad review on the KT-66 tone yet and they seem pretty affordable.
Man I love the way the lift control works. You can dial the amp for nice chimey tones, and then hitting the lift puts you in slight mid bump overdrive with a decent volume boost. Very cool. This is something I've wished my rocket could do. The nice thing about the lift too is that I've got it going through a mini pot so I can dial the amount of lift/boost I want. Good stuff. Now to get it switchable on a foot switch would be icing on the cake. I've tried to get Dana's foot switch circuit, but he hasn't returned my emails or PMs. Perhaps I'll look into relays.
The fat/normal/bright mod is no slouch either. It's great to dial in a muddy or bright guitar without messing with tone pots. Anyway, I think once the Reverb has been settled, and the amp gets burned in a bit, it's going to be a keeper. I'm sure I'll build a few more of these.
Now that the OD is solved, what is the main issue with the reverb?
Is it completely dead? I made the mistake on my first one of these build by leaving the white plastic spacer between the RCA jacks and the chassis, so the ground on the jacks was faulty. Removed the spacers and the reverb sprung to life
Simple mistake to make, but I wracked my brain for a few hours before realizing what I did.
I am looking at the layout you shared with me and it is very similar to the one that I drew up for the SSS amp. I don't see anything in the design that should keep it from working. I can't tell 100% from the photos if you followed your drawing so maybe it's a wiring error. I assume you have checked and it's not obvious at this point.
I tend to work in the divide and conquer method so I'll give you my 2 cents worth for free. Don't feel any obligation to use it. Using this you can figure out which piece of the circuit is dead, then you can find the problem.
1) Check the B+ voltage on your driver tube, recovery tube, AND the reverb transformer. Just make sure you have some juice in all those places.
2) Bypass the reverb tank and see if that tells you anything. Take the input from the reverb and put it directly into the output for the reverb and see if you you have a complete circuit. You can just make or buy a phono plug jumper to do this. Gerald Weber actually puts something like this in his book as an overdrive option. I think he puts something like a 100K resistor in between the in and out. If this works then its a reverb tank issue.
3) If that doesn't work, then try putting a preamp signal into the reverb recovery section by injecting a signal into the the phono plug using the reverb out cable from the tank. See if that tells you anything. Even the output from your walkman will be adequate to tell you if it's working.
4) If neither of these work, then I think it's trying to tell you it's in the reverb driver circuit. Start measuring voltages, swapping tubes, and looking for anything out of whack.
I've wanting to try Mark's switching scheme but haven't yet. I trust Mark's work for sure and I bet it is super slick. You'll have to report back on it.
The reverb issue has been resolved. And yes, it was do to a little newbie buffoonery. The reverb driver Rk calls for a 820 ohm resistor. I don't know how many times I looked at that schematic; and every time I read 820k. This afternoon looking over the schematic again, for the first time I saw an "R" instead of a "k". What a goob! Essentially, I had biased the driver tube so cold that it was pretty much non-functioning...or at least not able to amplify the signal at all. I quickly looked at my stock of resistors only to find a 1k2 as being the closest value I had on hand. I stuck it in there anyway, and badda bing...I got reverb. Sweet! What a lesson learned. Not only do you need to measure everything before installing, you need to double check to be sure you install what the circuit actually requires.
How does it sound? In a few words: subtly delightful. Perhaps the 1k2 is just the ticket, for the effect is not at all overbearing. Even when the reverb is dimed, it's usable. But you'd never play surf music with it. Not super glassy or strident. There is a touch of boxy midrange. I'll try some tweaking in the cathodes or return coupling cap.
Thanks Norm and Darin (and others) for helping to troubleshoot. Invaluable as ever; you guys are a tribute to what this forum is about!
Plus, I was thinking that if I can tweak this amp into some good tone with JJ's, then I should have a decent amp.
