Some "Dumbled" questions

[Aurora]

It's been a couple of days since I joined this forum, and it sure is alot of info crammed in here, albeit somewhat disorderly organized
I think I mentioned my purpose was to build an amp for my son - the aspiring guitarist ( he is actually quite good, but needs more serious band matching - and we live way out of the major city buzz)

I think I've more or less decided on the OD-101- full version, - but 50W for starters.
I've ben designing, building and servicing geophysical instruments and telemetry systems for over 30 years, so I'm not an electronics newbie. I've had one foot in the HiFI asylum for equally long, building, repairing and so on. I'm also very familiar with tube amps, KW transmitters, tube eqpt. in general - but I am a guitar amp novice ( I play woodwinds).
Reading my way through lots of posts, a series of questions cam up:

FET preamp
There are several posts indicating that the FET preamp is not very useful.
If included - would it be an idea to use a switch or relay to bypass the FET pre, instead of moving the jack plug?

Capacitors
Orange drops seems to be nirvana - but they are nothing more than polypropylene caps - no magic. Mustards are PE film caps, and by some concidered the european version of nirvana. As it happens, I have a lot of NOS mustards, and some Oranges.... and modern PP caps are a lot easier to find at this side of the pond than Oranges. Any thoughts or opinions?

Resistors
Seems like HAD relies onmetal films, which are of course very reliable and more long time stable than carbon comp, but I've noticed some concider NOS carbon comp almos as the "Holy Grail"?

Reverb vs. D'lator. or both?

Tube rectifiers vs. solid state?
It seems like "Dumbles" in general relies more on preamp distortion, and that "Rectifier sag" in this case is really not wanted ( less headroom) ?

"Normal" PCBs?
I can see that eyelet or turret boards give more room for experimenting than a traditional PCB, but if a is tested and "approved" - is no-one making e.g preamp boards as a regular PCB?
During the next 5-6 weeks, I'll have to spend quite a lot of idle time at work, judt hanging around waiting - while my eqpt ( except my PC) is locked up in running projects.. Is a PCB worth while, or just a waste of time?

Really hope some of you guys will take the time to answer..
That's it for now ... pro'ly more to come

[tubedogsmith]

As long as you're building I'd go ahead and do a 100 watter. It's really not much louder than a 50 and will have way more "girth" and depth to the tone and feel of the amp.

I really like the FET deal. A strat plugged into the FET input with the boost on is a very cool tone. Huge and sweet!

I quite often like a mix of caps in most amps and they are the sweetening on top but generally won't make or break an amp unless you're using something really weird. Same with resistors.

You can use a resistor in place of the choke to soften things up a bit so why mess with the extra expense of a tube rectifier. If you use a stiff power supply chance are your rectifier tube won't be rated to handle it anyway.

PCB's, go for it.

[ic-racer]

I think I've more or less decided on the OD-101- full version, - but 50W for starters.
FET preamp
There are several posts indicating that the FET preamp is not very useful.
If included - would it be an idea to use a switch or relay to bypass the FET pre, instead of moving the jack plug?

The FET is more for an acoustic. So, switching between FET and NOR would usually require a guitar change also

Capacitors
Orange drops seems to be nirvana - but they are nothing more than polypropylene caps - no magic. Mustards are PE film caps, and by some concidered the european version of nirvana. As it happens, I have a lot of NOS mustards, and some Oranges.... and modern PP caps are a lot easier to find at this side of the pond than Oranges. Any thoughts or opinions?

I think Speakers, Tubes, Circuit choice and component values will be the main things to get you in the ballpark on a first build. Component brand will have less of an effect.

Resistors
Seems like HAD relies onmetal films, which are of course very reliable and more long time stable than carbon comp, but I've noticed some concider NOS carbon comp almos as the "Holy Grail"?

I guess not HAD...

Reverb vs. D'lator. or both?

There will probably already be enough stuff to troubleshoot on a first Dumble build without including these. They are easy enough to add later through the effects loop.

Tube rectifiers vs. solid state?
It seems like "Dumbles" in general relies more on preamp distortion, and that "Rectifier sag" in this case is really not wanted ( less headroom) ?

I think once you start adding tubes and stuff, then component location gets changed and this affects lead dress which can cause hum or oscillations. The last thing you want is to spend all that time and money and find your amp has a hum you can't get rid of. ("Amp makes noise or hums" is a frequent post topic )

"Normal" PCBs?
I can see that eyelet or turret boards give more room for experimenting than a traditional PCB, but if a is tested and "approved" - is no-one making e.g preamp boards as a regular PCB?
During the next 5-6 weeks, I'll have to spend quite a lot of idle time at work, judt hanging around waiting - while my eqpt ( except my PC) is locked up in running projects.. Is a PCB worth while, or just a waste of time?

On a ODS 101 non-HRM build you may want to make ALL the boards PCB except the main preamp board. For the main preamp board, unless your traces are on top, it will be very difficult to flip it over and make any component change after the 35-or-so wires are connected.

Good luck!

In terms of component brand, sometimes it seems as if HAD used what ever he could get or had on hand at the time. Here is a chassis with some non-Orange Drop caps on the phase inverter and a carbon comp in the power section.

[Tonegeek]

Welcome to the forum!

Most of your concerns have already been discussed somewhere on this board but I can summarized some of it for you.

If you stick with what Dumble did, there is a better chance of getting help from the experts on this forum. I strayed on my first build and it cost me some time and frustration but worked out in the end. Also If you really want your build to sound like a Dumble then you will have the best luck using the parts that HAD used. There have been endless arguments about this or that cap/resistor sounds better but why take a chance? Save the experimentation for your next build. Trust me on this. Here's advice I got from Glasman (a respected forumite) given to me before I even joined this forum so I will pass it on:
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Orange drops, PS series. The 715 and 716 series just do not sound right in these amps. The XICON MPP is also an excellent choice. Dumble used pretty much what ever he had around in some areas of the amps. In other he was very specific. In his older amps he used PS series thought out. In the new amps he typically runs the XICON MPP and sometimes PS (or 715's) in the phase invertor. You can get away with 715's in the phase invertor as they do not impart that much "tone" in that section of the amp.I would recommend Vishay Dale RN65's for the plate resistors for the Clean and Overdrive stages. You can also use 1W carbon films and achieve very good results. The rest of the amp I would use a high quality metal film (I use KOA for my commercial amps) or 1W carbon films. 1/2 watt carbon films do not work as there is too much hiss. Also stay away from XICON metal films for the signal path. I might suspect that Carbon comps may be a little noisy due to the overall, gain of the amp.
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I would add to that to use ceramic caps for the pico values and Dales for the slope resistors. I think mostly around here people use carbon film in the signal path (except as mentioned above on the plates/slopes) Also, get low capacitance shielded cable for the areas that require it. And, I believe the supply resistors would be metal oxide or wirewound in some cases. Look at pictures of some real Dumbles and follow the wiring layout as it makes a difference. Study the threads on grounding (search on posts by DrZ400 and read grounding discussions on aikenamps.com) Use a separate tranny for your relay supply (the Dumble way). If it was me, I would start with a non-HRM amp. Read the discussion on HRM vs Non-HRM.

PCB might be ok, but not for the main board. Use a SS recto. The FET is not real popular. Same with the Jazz/Rock switch. Keep the Deep and Bright switches though. I build in my Dumbleator but the purist will argue it does not sound as good that way (I am very happy with my setup BTW). If you don't mind hauling around another piece of gear, then build it standalone. You most likely won't be able to use the loop without it. Many put the mid boost on a relay. I did that and love it. There is a way to combine mid boost and pre amp boost (PAB) on one really with a slight compromise. I got it working pretty well, but it is better to have them on separate relays.

My amps are 50 watters but there are good arguments for doing the hundred watter as previously mentioned here. The concensus is they do sound slightly better.

Good luck!

[Funkalicousgroove]

I've never seen Xicon MPP in a dumble- I've been in 6, and seen pics of another 5 or 6, I've seen 6PS, Nichicon mylar, NTE Mylar, and in one amp I even saw what looked like a couple Mallory M150's, but there was enough changed in that amp do question their originality. In older Dumbles there seems to be Metal film(mepco and dale mil spec)resistors for plates and cathodes, and in more recent amps 1/2w NTE 2% metal film.

I tried the 715 caps in the last coupling stage to the output tube grids and found them harsh and "hard" sounding.

[jelle]

I tried the 715 caps in the last coupling stage to the output tube grids and found them harsh and "hard" sounding.

+1!

Jelle

As for signal caps, I'd use polyester (mylar) caps. In europe the WIMA MKS4 types are readily available and they sound great. And yes, I have tried the 6PS orange drops too. Also great. Polyester it is!

Jelle

[brewdude]

Also, get low capacitance shielded cable for the areas that require it.

How do I discover the capacitance of a shielded cable?
How about using George L's guitar cable for shielded cable? I have a few feet that I'm not using lately. Would this be acceptable?

[tubedogsmith]

Also, get low capacitance shielded cable for the areas that require it.

How do I discover the capacitance of a shielded cable?
How about using George L's guitar cable for shielded cable? I have a few feet that I'm not using lately. Would this be acceptable?

George L works great if you pull the signal wire out and replace with teflon wire, basically just using the shield.

[Bob-I]

Also, get low capacitance shielded cable for the areas that require it.

How do I discover the capacitance of a shielded cable?

Just measure the cable. Set a capacitance meter on pF and measure 1ft of cable from shield to conductor. I haven't measured George L cable.

[brewdude]

Also, get low capacitance shielded cable for the areas that require it.

How do I discover the capacitance of a shielded cable?
How about using George L's guitar cable for shielded cable? I have a few feet that I'm not using lately. Would this be acceptable?

George L works great if you pull the signal wire out and replace with teflon wire, basically just using the shield.

Is the conductor wire on the George L's inferior? Is it that the insulator simply melts too quickly, or perhaps the wire is not safe for the high voltage?

[brewdude]

Also, get low capacitance shielded cable for the areas that require it.

How do I discover the capacitance of a shielded cable?

Just measure the cable. Set a capacitance meter on pF and measure 1ft of cable from shield to conductor. I haven't measured George L cable.

So, I cut one foot of cable. And measure pF from the center conductor of one end to the shield on the other end?

[fabiomayo]

I believe you get a more accurate measurement if you use greater lengths
and just divide your results by the distance in feet (or meters if you're
talking to one of us ).

[Funkalicousgroove]

George L is +/- 40pf/ft. A little high IMHO-

[brewdude]

George L is +/- 40pf/ft. A little high IMHO-

Can you please recommend a suitable low capacitance cable and where to source it?
I did see that Apex Jr. had a few different choices for shielded coax, but I couldn't figure out which one would be appropriate.
Is there a code to the part/model numbers?

[Tonegeek]

I've never seen Xicon MPP in a dumble- I've been in 6, and seen pics of another 5 or 6, ...

Maybe Gary knows something we don't know...

I tried the 715 caps in the last coupling stage to the output tube grids and found them harsh and "hard" sounding.

I could not evaluate the difference when I swapped the .1uF 715's for the .02uF PS on my PI plates, as I also was doing the whole Bluesmaster PI at the time. I don't mess with 715's anymore. The Xicon MPP's though seem to sound fine in these amps although I have only used them in a few spots and never in the whole amp. I know the PS sound good, so I don't stray much away from them. Not quite the rebel I used to be