New 100W Build - pics and a few questions

[wjdunham]

..

[dogears]

You need to use seperate filtering for each half of the loop tube. That way you can adjust the voltages accordingly. Check out the Dumbleator how to for tips. Try the alternate follower values in order to get 25-30V on the follower. Using the standard values it clips too soon, IMO.

Lastly, and this is important, you have a serious issue with your presence circuit. Do not attach the cap and 390ohm tail to the 3rd pot lug. Big no no. Go right to ground. Not pot!

[talbany]

If the hum goes away with the volume turned down on your strat or with humbuckers or with nothing plugged into the front end.. It's not the amp..Could be a grounding or shielding issue with the Strat..... Make sure your away from Dimmers, florescent lighting, your computer.. Even the transformers from the amp will cause singles to hum like mad out of the cabinet, sometimes up to 3 ft.
You really have to pay close attention to your layout when building an internal serial loop like the one you have as they can cause all sorts of noise related issues as well.. Hiss is normal..Nice Build!!


Tony VVT

[wjdunham]

First of all, thanks for the comments.
On the loop, I was going to change the follower values to 1.8K and 27K, just haven't gotten to that yet. I did an extensive A/B with my friends Fuchs, and the main difference was that the Fuchs clean channel is CLEAN, mine is a little less clean (looser?) for lack of a better description. The difference was subtle, and a matter of taste as to which sounded better. The Fuchs also had a little more crisp high end, I'm going to add the small bypass cap on the master vol to see if that gets me closer. I was thinking that maybe changing the follower values would clean things up a bit.
On the loop voltages, I probably should add the separate filter stages off the B+. I ran the follower off the V1 plate supply, the extra current lowered all my preamp plates 10V (200V down to 190V) which I think warmed the amp up a bit. I ran the recovery stage off the PI supply, which is why the plate is sitting so high, I'm just wondering if it's worth the effort to add the filter for that stage.

On the presence circuit, it must have been late when I wired that - it's that way on the DLite, clearly the 124 schem/layout shows the third leg not connected. Must have been looking at the wrong layout.

Tony, I would have drawn the same conclusion on the 60Hz noise (that it's the guitar not the amp) except that it seems to be worse with this amp than any of my others with the same guitar. I can definitely make it (almost) go away by positioning myself relative to the amp, but it just just seems very sensitive with this one, even with it switched to 50W mode. On a related note, I don't have any shielding on the inside top of the enclosure, do people typically put someing there?

I don't seem to be having any other noise related problems, but I do have to keep the loop return level way down or I get a lot of noise from my Quadraverb, right now I've got the levels set for unity gain through the loop, send level is pretty high, return level very low.

[talbany]

Placing some sort of shielding on the top part of the cab never hurts..Although I doubt that it will solve your problem... 60 cy hum from single coils is generally caused by stray electromagnetic fields emitted by a nearby transformer..It's really not that un common for one amp or set of transformers to produce a stronger or should I say larger field...Hammonds for instance produce a large field.. So do some Mercury Mags..Heybors are pretty good about it..The best transformers for this is believe it or not New Sensor 100 watt Marshall replacements..Nice and quiet all the way around.. Power transformers that use a copper strip down one side helps out somewhat but is not always a guaranteed fix either...Several things to try.. change the AC polarity... staple some copper flashing or screening to the inside front (behind the piece of wood with the grille cloth)..
Our amps have an open grille with wood trim in the front so I feel your pain..
Like Gil pointed out in an earlier post ..in a serial loop (which I assume you have) the return pot becomes the Master vol when you have the loop going..to get a nice fat meaty thicker tone run the master on the front at about half then control the volume on return..This might help out a bit with the noise you have in the loop... Keep the return on the low side... Just a suggestion...
Hope this helps!!!


Tony VVT

[wjdunham]

I am using Hammond transformers in this amp, that's one difference between this and my other amps. I figured as a first time builder noise and hum were going to be my big problems. Following the detailed layouts and some basic understanding of EM coupling seems to have kept me out of trouble so far.

One more question, is 185V getting too low on the preamp plates. It sounds pretty good after I raised the follower cathode to 30V, fixed the presence control and added a 30pf cap across the master. I can't play too loud at the moment so I don't know how much headroom there is, but at low volumes I'm pretty happy. I tried a few different tubes but don't have anything that will draw a little less current and let the voltage rise a bit.

Bill

[talbany]

One more question, is 185V getting too low on the preamp plates

That really all depends!!!For me I think with the 100k plate amps it's fine..However everything is a trade off.. 100k plate amps do tend to be a bit on the bright side so lowering the voltage down below 200 helps to warm it up a bit and gives it a nice organic feel interaction..However they will have a tendency with a not so cooperative tube compliment for the low end to kind of go loose on you as well as a slower gravel kind of breakup...Were talking in OD... I wouldn't go any lower and if you do keep it below 200v try some different combination's of tubes V1 V2.. You will know when you have found the right pair the amp will spit out a nice snarl..After you find it don't look back.. Good Luck

Newer tubes in general don't pull as much current as NOS or OS Just so you know!!

Tony VVT

[tubedogsmith]

did you grind the anodizing off the chassis around your ground points?

[BobW]

did you grind the anodizing off the chassis around your ground points?

Good point! I didn't see any over grind around the lugs, and believe the issue may be high resistance grounding.

[wjdunham]

I need to fix that. Most of the holes were on the small side so I had to enlarge them, and I relied on the contact between the screws and/or pots and the ID of the holes, probably not good enough. I checked all the grounds with an ohmmeter because I was concerned about exactly that, but that really won't show a marginal contact. Man, you guys are good

What did everyone do before Al Gore invented the interwebs, send Polaroids of their builds around?

[dogears]

That is an "f" up on the Dlite. There is nothing correct about it.

In any amp ever made, of any brand (as far as I know), the tail and presence cap are grounded and not connected to the third pot lug. The presence pot is a variable resistor and if you do the mistake, then it is not a variable resistor and you have parallel loads.

On the presence circuit, it must have been late when I wired that - it's that way on the DLite, clearly the 124 schem/layout shows the third leg not connected. Must have been looking at the wrong layout.

[ChrisM]

Sorry to go off topic here but what were your thoughts/opinions on the chassis you got?

[wjdunham]

I got out my grinder and hit most of the grounds, helped quite a bit, still not as quiet as my DLite, but it's a lot better. I really hit the chassis ground for the AC, a weak ground there could be a lot worse than just hum!

On the chassis itself, I have no major complaints. Aside from the "cheesy" factor of name silkscreened on the front... I had to do a lot of work sizing the holes for tube sockets and such, everything seemed like it was a bit on the small side. The 19" width made for lots of room even for a 100W setup. The finished amp certainly looks like the real thing if that's what you're after. I think the Brown Note chassis are the only other commercially available option, about the same price and higher quality. They are a bit smaller at 17" x 8".

[Structo]

Is that the chassis from the Asian guy?

I thought they looked good in his photos.

So the silk screened labeling isn't very good?

You are very adventurist to first of all build a 100 watt version then to top it off with a tube powered loop is cool.

These amps have many many things you can do as far as tweaking the tone or response.
Probably one of the most tweakable amps out there.

Hope you get the noise straightened out.

How is it with a humbucker guitar?

[dogears]

Tip:

Grail era degooped 100K plate amps have had either 10uf or 25uf bypass caps on both sides of V1. Disresgard what you have seen in other layouts. (there are 100K plate amps with 4.7uf as well, just none from the "golden era" that I know of)

For my $, the bigger bypass caps MAKE the tone of the 100K amp. I see you have a 4.7uf on one triode. Up it!

Try 22uf on both sides as well, to see what you prefer.

Also, is your cap on the bass pot a 102K or a 103K? Looks kind of big for a .001uf.