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Help with a Superlite IIb Parallel/Cascade
Posted: Wed 08/05/20 9:15 pm
by Bondoloso
I'm building a Superlite IIb (3/2011) with the Parallel/Cascade mod (2.2) from the skeleton of an old Voice of Music 566-A phonograph. Some of my voltages are out of whack, and I'd love some help. The following are the numbers I get in cascade mode.
EZ-81 (New)
Pins 1 & 7 = 311 VAC
Pin 3 = 310 VDC
A = 316
B = 265
C = 245
D = 220
V1 (Unknown strength)
Pin 1 = 148
Pin 3 = 1.26
Pin 6 = 112
V2 (PI) (Unknown strength)
Pins 1 & 6 = 184
Pins 2 & 7 = 38.5
Pin 8 = 54.8
V3 (New)
Pin 2 = 14
Pin 3 = 22
Pin 7 = 312
Pin 9 = 263
V4 (New)
Pin 2 = 22
Pin 3 = 21.8
Pin 7 = 297
Pin 9 = 244
Attached is the schematic. Forgive its piecework nature.
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Thu 08/06/20 4:04 am
by neikeel
I built one of these ptp in an old Elpico radiogram (lunchbox size). Like you I used the EZ81 and omitted the 100R sag resistor (not needed with tube rectifier). I used 32/32 can and 16/16 can fit filtering. Also used 820R/4n7 on v1b cathode. I also made my two inputs hi and lo like a 2204/2203 inputs rather than the cascade switch which is where I suspect your issue is.
Delighted with the results.
Have you tried known good preamp tubes?
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Thu 08/06/20 10:27 am
by geoff 1965
the 1st area standing out is your ez81, you're rectified voltage "pin 3" is the same as your HT voltage and should be higher.don't take it for granted being a new tube especially if it's a JJ! also if you can add some pics it helps with diagnosing sometimes.
good luck
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Thu 08/06/20 9:34 pm
by Bondoloso
Alas, it's a JJ. Damn the fall of the iron curtain. But if that's the issue, doesn't that push my voltages even farther out of spec? And like the first response, this is a lunchbox. I did try it with an 8ohm speaker initially and the volume was miniscule. And I got some motor-boating at one end of the gain pot. And some squeal when I cranked both the volume and gain. Is this an issue with a bad rectifier or something else. I'm at a loss for next steps..
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Thu 08/06/20 10:31 pm
by geoff 1965
the voltages on the schematic relate to a PT with 275 HT so your B+ voltages will be higher but you can drop that with a zener, sorting the rectifier will give you a target voltage to drop and also bring up your el84 plate voltages into the ballpark also your cathode voltage on them is too high but you can fine tune that and the motorboating issue later. focus on the rectifier and getting the B+ where you want it.
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Thu 08/06/20 10:38 pm
by Bieworm
I would try a SS rectifier. 4x UF4007 diode and a 10 watt sag resistor between 100 and 200 ohms. Fast and cheap way to know if your EZ81 is funky..
Heck you can even add a switch and have the option to select between SS or tube rectification
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Fri 08/07/20 10:09 am
by JMPGuitars
Bondoloso wrote: ↑Thu 08/06/20 9:34 pm
Alas, it's a JJ. Damn the fall of the iron curtain. But if that's the issue, doesn't that push my voltages even farther out of spec? And like the first response, this is a lunchbox. I did try it with an 8ohm speaker initially and the volume was miniscule. And I got some motor-boating at one end of the gain pot. And some squeal when I cranked both the volume and gain. Is this an issue with a bad rectifier or something else. I'm at a loss for next steps..
The problems you're describing sound like bad ground schemes, and parasitic oscillation. You can review the ground schemes/solder technique threads in my signature for guidance.
Regarding the oscillation, and probably some of the voltage issues, you need to use a wooden chopstick to move the wires around and see how that effects the noises. Fix the grounding scheme first.
Thanks,
Josh
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Fri 08/07/20 5:06 pm
by Bondoloso
Thanks for chiming in, fellas. I've tried to keep a good grounding scheme. The preamp bus is separate from the power supply. The mains ground is on a lug of the PT, the HT CT is on its own lug on the chassis and the filament CT is connected to the cathode bias input. For reference, in the photos below the top rail on the board grounds at the input jack, and the power rail is below it grounding to the downstream side of the cathode biasing resistor.
You'll see from the photos this is a very untraditional design. I was prepared to have some noise issues to sort out. I'm also prepared for plenty of razzing from you all. What's life without trying something different?
What would cause the el84 numbers to be so far out of spec? Also, when I test the PT without tubes, I get voltages in the 450vdc range. Is that helpful? I've got a brand new 12ax7 and another that's a known goodie, but I don't want to pop them in if I risk damaging them.
If my knowledge of electricity is sound, when I drop the current going to the power tubes, that should raise the overall voltage, correct? Will that be enough to bring things closer to spec? Also, any thoughts on values for the new resistors on pins 3 of the el84s to get that current down?
Amp 3.jpeg
Amp 2.jpeg
Amp 1.jpeg
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Fri 08/07/20 6:09 pm
by Bieworm
No offence man... but that wiring method is bount to give trouble IMHO. And you've burnt a lot of wires and components. You have to bring it to the witch doctor
I don't know what to say but , I would throw nearly all of it away and start over doing known and proven to be successful methods.
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Fri 08/07/20 6:28 pm
by JMPGuitars
Bieworm has a good point regarding the wires and lead dress. In addition to that, the ground from the socket MUST have it's own connection to the chassis, as close as possible to either the IEC socket, or cable entry point into the chassis (if not using a socket).
From your questions it sounds to me that you need to study the importance of lead dress, and how to troubleshoot an amp. You sound as though you're guessing, which is typical of beginners. One thing at a time, step by step. Don't jump from one thing to the next.
BTW- it also looks like some of the components are burnt, or possibly past their life expectancy.
Another thing Bieworm could show you is the difference between his messy first attempt at a specific amp build, and his complete do-over, and what a difference it made. Comparing the pictures looks like two different people made them, one being significantly more experienced than the other.
Thanks,
Josh
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 3:01 am
by Bieworm
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Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 3:51 am
by Bieworm
gotta give it to you, though.. even if it's a bad build, it is still built very complicated. Almost like a ship in a bottle
My worst build pics are somewhere on this site.. I posted them directly here and don't have them on my phone drive
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 11:46 am
by geoff 1965
i see what you mean by "lunchbox" things look tight in there but you should be able to sort it with some patience! just picking up on something you said "resistors to pins3 of el84's" have you one resistor in parallel with the capacitor for both el84's or have you a seperate resistor on each tube?
bye the way, if i stop contributing to this post it's because i've been listening to the singer in bieworm's guitar demo's! i've found some old rope and i'm looking for a suitable tree!!
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 11:58 am
by Bieworm
geoff 1965 wrote: ↑Sat 08/08/20 11:46 am
i see what you mean by "lunchbox" things look tight in there but you should be able to sort it with some patience! just picking up on something you said "resistors to pins3 of el84's" have you one resistor in parallel with the capacitor for both el84's or have you a seperate resistor on each tube?
bye the way, if i stop contributing to this post it's because i've been listening to the singer in bieworm's guitar demo's! i've found some old rope and i'm looking for a suitable tree!!
Why ??? Out of jealousy or out of repulse?
I took the modern classic to practice last thursday. Man I missed my TMB tremolo!!! For the classic to have a fair amount of dirt on low volume I have to push it with a boost pedal. The sad thing is that about every OD or boost pedal makes me dislike my amps sound. Without it sounds beautiful! But the TMB tremolo sounds sooooooo great without pedals and has plenty of OD by itself...
Are there suggestions for boost pedals that are a good marriage for the classic? Right now I have a mesa tone burst. A mucho boosto and a TS9. That TS9 is horrid on an 18Watt...
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 12:48 pm
by geoff 1965
Why ??? Out of jealousy or out of repulse?
neither,don't take my english "black" sense of humour to heart,actually i thought the trem/breakup of the guitar was very good!
have you tried a boss BD2?
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 1:04 pm
by JMPGuitars
Bieworm wrote: ↑Sat 08/08/20 11:58 am
Are there suggestions for boost pedals that are a good marriage for the classic? Right now I have a mesa tone burst. A mucho boosto and a TS9. That TS9 is horrid on an 18Watt...
Those are all overdrive boosters, right? Get yourself a clean boost. I built an EHX LPB2 replica into my PRS as a 20db clean boost, and it works awesome. The Stratoblaster is a fairly popular booster as well.
Using an overdrive/distortion booster, you're stuck with the tone/tonesuck of the pedal. With a well made clean booster, you're pushing the amp harder to get your distortion sound.
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 1:47 pm
by Bieworm
geoff 1965 wrote: ↑Sat 08/08/20 12:48 pm
Why ??? Out of jealousy or out of repulse?
neither,don't take my english "black" sense of humour to heart,actually i thought the trem/breakup of the guitar was very good!
have you tried a boss BD2?
Ah ok!!! I thought you were refering to our band singer
No I haven't, but I know someone who has one. Thx for the tip. ... but either way.. the TMB is all I crave for. Wish it was in the classic combo shell. But I have to unwire everything to switch chassis to do that... pffff
I like the front control panel better... but that houses the classic.
15969124765551792387499939923007.jpg
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 2:48 pm
by Bondoloso
Great advice from all. Thank you. As you've deduced, I am relative newbie. This is my second build after a tweed Princeton clone from an ancient GE phono. It's nice to know I'm not alone in wonky early builds, though even Bieworm's first try looks fantastic compared to mine.
I've been worried about the lead dress from the start. But with so little space and a zillion rewires due to pins on two tube sockets cracking off at the base on the last wire solder, I wanted to at least see if I could get things working. Looks like I'll be better off starting over.
Geoff, I misspoke about plural resistors on pin 3 of the power tubes. It's a single cathode resistor. As for the scorched wire and parts, all the values check out, and I can't see any bare wire even with a magnifying glass. But I'm going to rewire most of it now, so that will help.
Just to make sure I get everyone's suggestions (and thank you again):
*Cleaning up the lead dress should help with the noise and could help with the motor boating. (Any suggestions for how to do that when all the controls are on the top half of a two-piece frame? Should I use shielded wire for everything? I need to have a connector in the middle or otherwise I'll never be able to slide the two pieces apart unless I drop the entire harness--or maybe that's a better option?)
*Get a new EZ81 that isn't a JJ or switch to diode rectification. (I thought rectifiers were either good or dead, and there isn't usually an issue with what we see here where the ac and dc voltages are nearly identical. There's nothing in my wiring or the specs of the downstream parts that would account for the drop in DC, right? I'm not sure I understand that well enough.)
*Decide whether I want to stick with the cascade/parallel switch or use two inputs.
*Don't use a tube screamer or overdrive with an 18W, rather go with a clean boost. wink
*Avoid listening to Bieworm's demos without suitable PPE. winkx2
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 4:33 pm
by Bieworm
Bondoloso wrote: ↑Sat 08/08/20 2:48 pm
Great advice from all. Thank you. As you've deduced, I am relative newbie. This is my second build after a tweed Princeton clone from an ancient GE phono. It's nice to know I'm not alone in wonky early builds, though even Bieworm's first try looks fantastic compared to mine.
I've been worried about the lead dress from the start. But with so little space and a zillion rewires due to pins on two tube sockets cracking off at the base on the last wire solder, I wanted to at least see if I could get things working. Looks like I'll be better off starting over.
Geoff, I misspoke about plural resistors on pin 3 of the power tubes. It's a single cathode resistor. As for the scorched wire and parts, all the values check out, and I can't see any bare wire even with a magnifying glass. But I'm going to rewire most of it now, so that will help.
Just to make sure I get everyone's suggestions (and thank you again):
*Cleaning up the lead dress should help with the noise and could help with the motor boating. (Any suggestions for how to do that when all the controls are on the top half of a two-piece frame? Should I use shielded wire for everything? I need to have a connector in the middle or otherwise I'll never be able to slide the two pieces apart unless I drop the entire harness--or maybe that's a better option?)
*Get a new EZ81 that isn't a JJ or switch to diode rectification. (I thought rectifiers were either good or dead, and there isn't usually an issue with what we see here where the ac and dc voltages are nearly identical. There's nothing in my wiring or the specs of the downstream parts that would account for the drop in DC, right? I'm not sure I understand that well enough.)
*Decide whether I want to stick with the cascade/parallel switch or use two inputs.
*Don't use a tube screamer or overdrive with an 18W, rather go with a clean boost. wink
*Avoid listening to Bieworm's demos without suitable PPE. winkx2
Beware .. my replies aren't meant to be cruel. Above about the singer-thing was a joke from my side too. I thought Craig was referring to a practice demo with our band singer.
FWIW I have spent hours resoldering and rewiring to get rid of a noise.. it turned out to be a new faulty EZ81 (a JJ ofcourse). I converted it to SS and the noise was gone. But I must mention that was a popping crackling noise
Re: Help with a Superlite IIb Parallel/Cascade
Posted: Sat 08/08/20 6:29 pm
by geoff 1965
okay and is the el84 bias resistor 150 ohms as per schematic? one test you can do is switch on and after 5 mins measure the cathode voltage and monitor it to see if it's stable or gradually creeping up.
is the squealing you mentioned happening in cascade mode or both? you might just need to attenuate the signal.
take your time and be safe working around with voltages present.
as for bieworm's singer i saw a good film with Kirk Douglas where he plugged his ears with bees wax to stop him going crazy!!
i know your'e limited for space but one area of lead dress is making sure plate leads don't touch signal leads going to the tubes.
keep at it and good luck
