NOS Sprague PS Dark Sounding?

[Charlie Wilson]

Hello, I just finished building a Low Plate Classic and it sounds good but it is kind of on the dark side. I used new components except for the .1 coupling caps. I bought a bag of NOS on Ebay and used those. I guess I didn't like seeing CDE on the side of my caps. I read a thread were someone said NOS Sprague would be darker and sweeter sounding but I did not think they would be this dark. I choose this circuit because I play Fenders and I thought it would be a lively sounding amp. Anybody have experience using old caps and should I be investigating other possibilities? I did try different tubes and a GE as V1 helped but I still think this thing should not sound quite this dark.

[talbany]

Charlie

IMO...The NOS Spragues vs the new CDE's (with no time)we get today can be only slightly darker but really not that noticeable and shouldn't be why your amp sounds dark..I thought the difference was so slight I think the added expense using NOS Sprague caps were not even worth the effort,in a D-style

BTW..For those looking for scientific proof of this..Good luck getting it,,
This is just what my ears tell me, comparing the 2

Tony

[67plexi]

Charlie, My first #124 skyline is dark sounding. I used new production power tubes
I did not use a CTS 2-35 treble pot. I did use a 1971 Fender Twin OPT.
One easy fix would be your bright switch. Replace the on-on switch with a on-off-on
and try a 250pf & 500pf silver mica 500v or just try different values of silver mica capacitors to taste.
My second #124 Classic build I used exact parts as the original and all NOS tubes
1959 Twin PT 1971 Fender Showman OPT 4/8 ohm taps in a combo sounds great
EVM12L . One other place you may want to go is your V-1 voltages #124 was 185v go to 195v
To me the most important tube in the amp is the PI I use 1962 10,000 hour life tubes with matched
sections. Charlie if you need a CTS 2-35 treble pot let me know.
And on the plates I can send you Mepco/Electra MF7C 1% it all makes a difference.
I'm sure others will chime in on their thoughts . Look at real Dumble builds from the 1980's
and see what parts were used.

Steve.

[Charlie Wilson]

Thanks Tony. Wow, Steve I would love to take you up on the 2-35 pot and resistors. I will PM you to discuss that further. I did do a two way bright switch with a 100pf and 300pf cap and it does definitely ups the treble. I especially like the 100pf with the deep switch on with the Strat. It just seems to me the amp without the bight switch should be brighter with a classic tone stack and 100k resistors. The other thing I notice is that the presence control is pretty subtle. Maybe I need to check NFB issues. What is a little frustrating is that the amp does sound pretty good. I almost wish it had some gross issue or sounded bad. It might make it easier to find an issue. I guess I need to get in my Zen space and consider it a challenge rather than a struggle.

[talbany]

Charlie
IMO.. I don't believe there would be much difference in the brightness of an amp by going from your RN-65's to the older mepcos (I've used both)..I do think the mepcos are smoother in the upper frequency's and less 3rd harmonic order.. As far as the treble pot goes I don't think the 2-35 has that much effect on the brightness other than where you set it and the taper since it's just basically a mixing pot between the bass frequency's and the treble frequencys..You may have to set it a bit higher to get the same effect as the 2-35 but this pot should have very little effects from loading..If the amp is dark on the clean channel I would double check the value on the 220k/ bypass cap in the grid of V1-B..You could maybe up that value and replace the treble cap in the stack to a mica..You could also up the value on the master bypass cap..Definately try some different value NFB resistors..This is where I would start..Also upping the voltages from 185 to 200V on V1 will increase the brightness some but it is IMO very subtle..I would still take Steve up on his pot and resistor offer..
BTW..Low Plate classics are inherently bright amps when working properly, so there could be a wiring error or an out of spec part somewhere..

Good luck!!

Tony

[Charlie Wilson]

Thanks for those suggestions Tony. I never thought about the cap across the 220k resistor. I think the plan is to carefully re-check correct wiring and good connections per the layout, swap out the .1 NOS orange drops with new ones (the ones I got did look a little beat up), and then changing out some things as suggested. I thought that was very cool of Steve to make that offer so I will definitely take him up on that. I'm curious about a bright cap across the master volume. The layout for the Low Plate Classic doesn't have one although I know you have stated in the past, there is no right or wrong, whatever works. I just assumed that #124 prior to the skyliner upgrade was a bright amp and didn't need one. I have tried clipping some across the master and it does make it brighter but I just want to make sure that I am not putting a Band-Aid on some other issue that I need to sort out.

[ToneMerc]

I 've built maybe 8-10 amps ( classics and skyliners) with the period correct caps and resistors, I agree with both Steve and Tony.

TM

[talbany]

Charlie
That's right..The low plate classics are generally bright and lively amps to begin with and don't normally need bright caps across the master (if you use the loop or not)..Generally things like voltage and NFB tweaks are to help tame the brightness (in the case of a really bright amp) and not usually thought of as trying to add brightness to them (if that makes any sense)..At the same time I don't believe that changing resistor types and pot types can turn a dark lifeless amp into a bright and lively one,they are just too subtle..IMO...I have a feeling there is something else going on that is causing that amp to be dark and lifeless..Without hearing it it's hard to say what that might be and where to look.

Again Good Luck!

Tony

[67plexi]

I'm not thinking straight I lost my daughter Anna last month just turned 23
Looking at the photo of the amp first place I would go is get rid of that 330pf ceramic capacitor
and change it with a SBE .0022uf = 2200pf that should boost your cleans.
Next the 4k7 negative feedback resistor go 3 watt not one watt.
And if that doesn't fix it a full amp voltage chart would be the next step.

Steve.

[Charlie Wilson]

Steve, I am very sorry to hear that. A piece of aluminum with some tubes sticking out of it doesn't seem very important when you hear about someone going through that. I got home ready to start pulling things out of my amp and decided to spray a little Deoxite in my female to female adaptor I use to plug my amp into the speakers of my Pro Reverb and my amp now is rather bright. I feel like a bit of a dummy. Thanks you guys for the help. If the next amp I build is dark sounding I have some solutions and Steve I am very sorry for your loss.

[M Fowler]

Steve, sorry for the loss of your daughter.

Mark

[talbany]

Steve
Sorry to hear about your daughter!!

Tony

[mhartman]

Steve,

I'm sorry to hear about your loss. I have two daughters and can't imagine losing something so precious.

Mike

[bluesfendermanblues]

Steve, Sorry to learn about your loss.

[CHIP]

Steve, You have my condolences.