Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Guitarzan on August 03, 2014, 02:15:15 pm
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Hiya!
I just scored a Newcomb M-5 on fleabay and was wondering if anyone else has had any experience with one of these. According to radiomuseum.org, it's 4.5 watts which should (in my mind) put it in the same realm as my 5F1 Champ but I tried it out and it doesn't get anywhere near as loud as the Champ. It's cute as a bug's ear tho. Here's the link to it on radiomuseum...http://www.radiomuseum.org/r/newcomb_guitar_amp_m_5.html. (http://www.radiomuseum.org/r/newcomb_guitar_amp_m_5.html.)
I was planning on going thru it and replacing caps and resistors as needed but if anyone has any ideas for what to mod on it to get the volume up there closer to the 5F1 I'd really appreciate it. I hope I got the schemo attached properly.
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put a boost pedal, or any pedal that can give like +12dB or more of clean gain. See what you get. the 6SQ7 is most likely not giving you enough gain. If more out front gain wakes up the amp, you might put a bottle in front of it,, or swap it out for a 6SL7 and use both triodes for gain....
Depending on the secondary winding that might be a lot of NFB to keep it clean and stable. disconnect the NFB temporarily, see what it does.
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put a boost pedal, or any pedal that can give like +12dB or more of clean gain. See what you get. the 6SQ7 is most likely not giving you enough gain. If more out front gain wakes up the amp, you might put a bottle in front of it,, or swap it out for a 6SL7 and use both triodes for gain....
Depending on the secondary winding that might be a lot of NFB to keep it clean and stable. disconnect the NFB temporarily, see what it does.
I checked on that but the 6SL7 won't sub for the 6SQ7 which is a triode/dual diode.
I have a tube screamer I could try. Not sure of how much clean boost it'll provide tho.
Also, I should prolly mention that I have the harp player across the street in mind for this one. He bought one of my 5F1 builds and loves it. He calls it his luchbox & has gigged with it about 50-60 times over the past year. So I figured if he loves the tweed champ in part for it's size, then he'll flip over this thing since it's much smaller and lighter than a champ. It just doesn't seem like it's putting out anything like 4-1/2 watts.
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tone stack & filter at input has significant loss, NFB adds some loss.
disconnect tone-stack & disconnect NFB.
see attached schema for suggestions.
--pete
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DummyLoad,
I will try that. Thanks very much for the drawing. I'll post the results back here as soon as I get this accomplished. I think it'll be Tuesday though. My son is coming home from hospital tomorrow & I don't think I'm gonna be able to work on anything until late tomorrow or more likely Tueday morning. I knew the tone stack could cause some loss but I had no idea it could be that pronounced. This thing wide open is like my champ on about vol-2.
Thanks again!
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This is a phonograph amp, not a guitar amp. (I think RadioMuseum is wrong.)
Geetar is weaker than (old-style) phono pickups. You need one more stage of gain.
> same realm as my 5F1 Champ
You note that triode-preamp Champs have *two* triode gain-stages (or a hi-gain Pentode) before the 6V6.
You aren't boosting the guitar enough to SMACK the full several-Watts out of the 6V6.
We can estimate input sensitivity from hoped-for output and NFB network values. 4W in 4 Ohms is 4 Volts. 2700/100 is gain of 28. 4V/28 means 0.14V or 140mV needed at the input to get 4W output. Guitar amps are usually shimmed to need only 20mV input for full output. 50mV sensitivity (very early amps, Swing era) won't rock-out well (OK for polite rhythm work).
Like my backhoe- it has 20HP of yank, but the control lever linkage is loaded so I can't pull hard enough to get full hydraulic yank when the hoe is far off-side.
That tone-network isn't doing much loss when full-up.
The actual sensitivity is less than calculated above (the NFB loop isn't doing much). 14.5V peak 10V RMS at 6V6 grid, gain of 50 in 6SQ7, means 200mV input needed. You gonna need a HOT pickup and a handful of rage-pills to strum your axe near 200mV more than a few moments. That's working too hard. That's what amplifiers are supposed to do for us.... you need more low-level amplification.
Short answer: put a boost pedal in front. LBP is a classic. Mild fuzz turned-down out of gross fuzz would do.
Long answer: re-wire the first hole for a 2-stage 12SL7 6SL7 preamp.
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why 12SL7? heater shows 6.3V winding?
--pete
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PRR,
Thanks a bunch for that eval. I have seen a bunch of your posts to other guys looking for advice and was hoping you'd chime in on this one.
I have never modded or built from scratch. Only done kits up to this point. So bear with me if I sound ignorant, it's only because I am.
So why do you specify a 12SL7? Wouldn't a 6SL7 be appropriate? The 6 or 12 in this discussion is the filament voltage isn't it?
Also, would I refer to a champ 5C1 for how to wire that tube socket? I'm not great with schematics, but the 5C1 looks to me to be almost exactly like the Newcomb if the tone stack was taken out like DummyLoad suggested.
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I did manage to get it opened up and had a look inside. Newcomb used a pot with a switch on the tone and volume. So if I did lose the tone stack, it would be a simple matter to move the power switch wiring over to the volume pot ala champ.
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I checked on that but the 6SL7 won't sub for the 6SQ7 which is a triode/dual diode.
no it won't, that'll require rewiring the socket, and adding a few components to provide a 2nd triode. I suggested a 6SL7 because its the highest gain twin-triode octal that you can round up for a couple of buck$. The 6SQ7 is only a single triode,.. Its' like 1/2 a 12AX7. for guitar, you want a full 12AX7,, or a 6SL7 if you want to stick to octals.
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we run 12a_7 all the time off of 6.3vac filament supplies...
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Hello to all.
I'm thinking that if I'm going to start rewiring stuff in there, I might as well go all the way and convert it to a 5C1-type of circuit. Any thoughts on that plan?
There is one other possibility that could change things tho. I saw a 12AX7 to 6SQ7 adapter on eBay and was wondering if anyone knows anything about these and whether or not I can actually just plug it into the amp, plug a 12AX7 into it, and be good to go. If not, then I think the 5C1 is gonna be the plan.
So...the next questions I'll need to get answered are:
#1 Will the current PT be able to handle the 5C1 tube lineup? I'm guessing the answer is yes since it can handle the existing 3 tubes, but figured I'd better ask to be sure.
#2 Can I use the existing cap can rather than trying to cram the 3 filter caps in that teeny chassis?
#3 If the cap can will work, do I have to adjust the value of the associated 2-Watt resistors?
#4 Will the existing OT still work with the 5C1 changes?
I have a set of ClassicTone 5F1 trannies (I think it's the same ones for 5C1) here so I could use one or both as needed but the existing PT is also tiny, just like everything else on this unit. However, I believe it could work, but it's gonna be a bit of a squeeze as it is. I don't want to have to try and fit a larger transformer on it if I can help it.
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The M-5 schemo didn't take. I tried to attach it with the 5C1 docs but it didn't go for some reason.
so here it is
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Actually on those resistors, it looks like most modern schematics (as well as the 5F1 kits I built) use a 5-watt and and a 1 or 2 watt and NOT 2-watt in the filter.
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#1 Will the current PT be able to handle the 5C1 tube lineup? I'm guessing the answer is yes since it can handle the existing 3...
yes, 6SQ7 draws 150mA and 6SJ7 draws 300mA. additional 150mA should't be a problem.
#2 Can I use the existing cap can rather than trying to cram the 3 filter caps in that teeny chassis?
yes, assuming can cap filters are still good though...
#3 If the cap can will work, do I have to adjust the value of the associated 2-Watt resistors?
no, just change the 6SQ7 to 6SJ7: add, screen resistor and screen bypass cap, change cathode and plate resistors to 5C1 values (or close standard values). the newcomb shows 275V supply to triode and 5C1 shows 280V: the difference is negligible. you may need to adjust 12K resistor to get close to 280V supply to 6SJ7 as in the 5C1 and if you do, a higher wattage rating won't hurt.
the filaments move from 7 & 8 (6SQ7) to 2 & 7 (6SJ7). the schematic shows one side of the filament secondary grounded.
on the 6SQ7 socket you have either pin 7 or pin 8 tied to ground at the socket.
a) if pin 8 is grounded, then lift it off ground as pin 8 becomes the plate; now ground pin 2.
b) if pin 7 is grounded, then move the filament supply wire to pin 2.
#4 Will the existing OT still work with the 5C1 changes?
irrelevant to the changes being made.
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I saw a 12AX7 to 6SQ7 adapter on eBay and was wondering if anyone knows anything about these and whether or not I can actually just plug it into the amp, plug a 12AX7 into it, and be good to go.
I'm not what they might be doing with such a connector other than using only a single triode of the 12ax7 wired to the 6sq7's triode (and ignoring the 6sq7's diodes). It the end, your circuit is wired for a single triode. both the 6sq7's triode and a single triode of a 12ax7 has a max Mu of 100, so .... it'll do nothing really...
If not, then I think the 5C1 is gonna be the plan.
I second (or third!) the motion to "just re-wiring the 6sq7 socket to accept a 6sj7"
follow Dummyload's rewiring, also ground pin1 (the shield). make sure you have a coupling cap between the grid and the guitar and you should be good to go.
I'd use the transformers as-is.
After that, see where your at gain/volume wise,, and then plan the next move (if needed).
#2 Can I use the existing cap can rather than trying to cram the 3 filter caps in that teeny chassis?
#3 If the cap can will work, do I have to adjust the value of the associated 2-Watt resistors?
I'd start AS-IS. once running, you can measure voltage drop across resistors to see how close to the resistor's wattage rating you happen to be.. (or over..).
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6sj7 in 5C1 is drawing ~650uA.
looking at the schematic, i think 90V is stated at the plate of 6SQ7 with 275V supply.
6SQ7 is drawing 185V/470K or ~390uA
45V drop across 12K is 3.75mA @ 168mW; that's screen current + 6SQ7 load of 390uA. so screens are pulling 3.75mA-390uA=3.36mA
new load is 3.36mA+650uA=4.01mA @ 185mW
45V/4.01mA=10.9K replace 12K with a 10K 1/2w -or- just leave it and live with a slightly lower supply voltage to 6SJ7.
--pete
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#2 Can I use the existing cap can rather than trying to cram the 3 filter caps in that teeny chassis?
yes, assuming can cap filters are still good though...
In addition to it being quiet due to low gain, it's really very quiet as it pertains to hum. No hum at all really. In fact it sounds quite good save for the way too low gain situation. The clean sounds chimey and open until about half way up on the volume pot and then it distorts nicely the rest of the way up. It would make a good bedroom amp. Really bedroom...not like the 5F1 which is way too loud (IMO) for bedroom volume when you want it to give up that tube distortion.
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I want to thank all of you guys who've replied to this thread. i truly appreciate your input and will let you know what my results are when I make the changes.
that cap can also has the 25/50 cap for the 6V6 in it. I'm assuming I can also reuse that. I do have caps of that flavor in my boxes of stuff, but again, space is going to be an issue if I start trying to cram "normal" sixed parts in there. As I mentioned, the thing is loaded with mini-components. Evidently, that was how they managed to make the finished product about the size of a Batman lunchbox.
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I'm getting some 6SL7s from a guy who wants to know if I have a preference for brand, black or grey plates, siver dome, etc. I have no experience with this tube so I don't have a clue how to answer those questions.
So what do you guys like?
If there are common drop-in subs that can experiment with, what would they be?
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RCA red base 5691; sylvania chrome top with black round or triangular plates; tung-sol shorty's with the smoke glass.
--pete
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"12SL7" was a typo. Sorry.
> we run 12a_7 all the time off of 6.3vac filament supplies...
12AX7 and kin have a tapped heater which can run on 6V -or- 12V.
Two separate triodes plus a tapped heater means 9 pins.
This chassis has Octal (8-hole) sockets. And 6V heat supply. He wants the 6 Volt version of a two hi-gain triode. This would generally be 6SL7.
(6SC7 seems suitable BUT both cathodes are tied together. This works fine for many things, but not for sequential gain stages.)
He can of course fill the Octal hole and punch it for a 9-mini socket, use the familiar 12AX7.
One Pentode "can" give the required gain. However that much up-front gain can overload before the volume control. All the one-pentode-preamp amplifiers faded for twin-triode plans.... they handle much wider range of input levels. However pentode preamps do have fans.
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Here's a shot of the innards for anyone who might be interested...
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He can of course fill the Octal hole and punch it for a 9-mini socket, use the familiar 12AX7.
Is there an "official" piece of hardware to do this? Or would I just have to put a "patch" over the octal hole and punch it for the 9-pin mini?
I'm starting to think about just going for the 12AX7 since I have a bunch of them already. I have a bunch of sockets, & tube shields too.
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Weber has an adapter for this. Will it work with your size octal hole? I don't know.
I would probably stay with the octal socket and rewire it for a 6SL7. Look at some old Ampeg schematics for some good sounding circuit options.
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cool looking little chassis...
my vote gets the 6SL7GT: no machining involved.
if it were mine: i'd remove the pot closest to the chassis edge and replace it with an input jack: the hole size is the same. leave center pot and AC switching alone.
attached is a simple champ circuit i'm fond of... whatever you decide, keep us in the loop.
--pete
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Pete,
I will definitely keep you guys posted on this. Thanks again (and again) for all of the advice and schemos and everything.
I do like the idea of going with the octal preamp tube for the simple fact that the socket is already there. I've been browsing all sorts of web pages regarding this stuff and found quite a few folks reprorting octal preamps tubes having a tendency to going microphonic. That was why I began leaning toward the 12AX7. I've run into some 12AX7s that were microphonic tho, so I doubt it's anything unique to the octal tube. Only I have a box full of 12AX7s and not a single 6S*7 in the house. Not the end of the world tho. Then I read that the 6X5 tends to be a problematic rectifier so I started thinking of going with a 5Y3** which I also have a slew of in here. However, that little tranny doesn't have any 5v secondary so it would mean (ugh) even more machining to make a champ tranny fit.
So I guess I'm going to have to get hold of a few 6Sl7s or equivalent and just do it that way. It seems to be the concensus on this board as well.
BTW, I couldn't open the attachment with the .sch ext. Do you have it in any other foramt?
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BTW, I couldn't open the attachment with the .sch ext. Do you have it in any other format?
Here's a link to download the free .sch program.
http://el34world.com/Forum/index.php?board=12.0 (http://el34world.com/Forum/index.php?board=12.0)
Brad :icon_biggrin:
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Guitarzan, just 2 quick things from a guy not all that experienced. First, I love the 6SL7. I think they sound very sweet, and the sockets are easier to wire cuz they're bigger. :icon_biggrin: Nothing wrong with the 12ax7 though, they don't sell a million amps with them because they're not any good. And don't worry about installing a filament transformer, just use a couple diodes, the 1N4007s will be fine, in place of the rect. tube. If you want to have the sag of the tube, but want some protection just wire the diodes in series with it. Just my 2 cents.
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cool looking little chassis...
my vote gets the 6SL7GT: no machining involved.
if it were mine: i'd remove the pot closest to the chassis edge and replace it with an input jack: the hole size is the same. leave center pot and AC switching alone.
attached is a simple champ circuit i'm fond of... whatever you decide, keep us in the loop.
--pete
Hey Pete...
This Newcomb mods pdf looks simple enough for even me. I like it. I'm going for it.
I thought about leaving just a volume/power switch per your vote, but I think I'll keep the tone control too. I have some appropriate silver mica caps that I can use there and I was thinking along the lines of a 5F2a type since from what I've read all over the place, it is a low loss setup and I just want something different from a champ type of amp for this project.
Sure, it's still basically a 5C1 with tone stack, but...y'know...
So my very first idea for this thing was to add an input jack on the other side from the pots. It'll go right next to the preamp tube. You have to open the back to use it anyway and the little face-plate on the front says tone and volume so that'll keep that part of it stock. I found a Jensen P69R for 25 bux delivered. The stock speaker has a torn surround anyway so out it goes.
I don't doubt that as PRR said, it's likely a record player amp, but I think Newcomb took an amp that they already had on the shelf and made this setup out of it. The patch cable has 1/4" phone plug on the one end, and is hardwired in the chassis, plus it shows the 1/4" plug on the schemo. So whether they had guitar amp in mind, or just some a powered ext speaker for something I don't know. But I have no doubt it came from the factory just the way I got it.
A grounded power cord will also be in the plan. Whether or not I put one of those IEC connectors in there, I still haven't decided.
So thanks again for everything. I knew I'd get good answers to my questions here. As I have researched other projects along the way, I'm consistently directed to this board by Google and have always found the members to be great in the way they make really good suggestions, and make 'em understandable for guys like me. Very friendly bunch here. :worthy1:
I'll take some pix along the way and post 'em with progress reports. It's the least I can do in return for the help. You should be kept in it as it's really your project to in a way.
TTYL
-d {8^)
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GZ, happy to help.
if you're going to drill another hole, suggest moving both pots closer to the center and use the hole at the edge (where the tone pot is now) for the input jack. the input jack should be as close as possible to V1.
leave the AC switching on the tone pot: switch neutral. take the neutral wire from IEC to switch on the tone pot then to PT. the hot goes from IEC to fuse, out of the fuse to PT. if you decide not to cut for an IEC, then just enlarge the strain-relief hole to accept and 18/3 power cord and 18/3 size strain-relief.
i updated the schematic.
good luck! :icon_biggrin:
--pete
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Yeah! That's pretty close to the way they wired it.
I'm not used to seeing the neutral switched. I used to wire homes for a living and you never switch the neutral in that world.
BTW, Where I was talking about drilling for the input jack is actually closer to v1 than putting it in the pot hole.
I appreciate that you have my back tho.
Thanks for the mains tip and the updated docs!
Just for your review, here's a gut shot with the phone plug right in the neighborhood where I'm talking about putting it. v1 is in the upper right corner.
I tried to get a shot of this weird little wafer thingy (cap?)
I've never seen one like that before. It has about 6 wires coming out of it.
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I goofed up the attachments again and only got 1 of 'em.
Here's the one with the proposed input jack loc.
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I tried to get a shot of this weird little wafer thingy (cap?)
I've never seen one like that before. It has about 6 wires coming out of it.
It's a pre made circuit. Ampeg used them in the tone stack in some of their amps.
They were made for company's to wire up amps and other things faster, less solder joints.
Brad :icon_biggrin:
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I tried to get a shot of this weird little wafer thingy (cap?)
I've never seen one like that before. It has about 6 wires coming out of it.
It's a pre made circuit. Ampeg used them in the tone stack in some of their amps.
They were made for company's to wire up amps and other things faster, less solder joints.
Brad :icon_biggrin:
no kiddin' hmph. I'll have to figure out what part of the schemo represents the thing.
I thought it was probably an OEM sort of thing cuz it only has the numbers 1-8 on it. I No mfd or ohms symol or anything that might identify it otherwise.
I think there are 7 wires. I think it skips a number so there's like, 1-5 then 7 & 8 or something like that. I'll get a better look at it when I start de-soldering tomorrow
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I tried to post a highlighted pic of an Ampeg B-15's tone stack circuit but I'm unable to do it. :BangHead:
Look in Doug's schematic library of an B-15 and the part of the tone stack that is in the dotted lines (caps/resistors) is like you have.
Here's a link;
http://el34world.com/charts/Schematics/files/ampeg/Ampeg_B15N.pdf (http://el34world.com/charts/Schematics/files/ampeg/Ampeg_B15N.pdf)
Brad :icon_biggrin:
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I bet it's a multi-section capacitor. Recently I got a couple included with a bunch of TV parts, they were set up in just like that. Test it with capacitor checker, or you may find a part number on it, you should be able to figure it out.
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I tried to post a highlighted pic of an Ampeg B-15's tone stack circuit but I'm unable to do it. :BangHead:
Look in Doug's schematic library of an B-15 and the part of the tone stack that is in the dotted lines (caps/resistors) is like you have.
Here's a link;
http://el34world.com/charts/Schematics/files/ampeg/Ampeg_B15N.pdf (http://el34world.com/charts/Schematics/files/ampeg/Ampeg_B15N.pdf)
Brad :icon_biggrin:
The part of mt schematic that's in the dotted rectangle is definitely the cap can. It says CE-36 (I think) under it.
The pots have individual caps and resistors soldered on and that chip thingy is soldered to V1 and V2 so I don't think it's part of the tone stack.
I dunno...I s'pose I'll have to get it nailed down tho.
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I bet it's a multi-section capacitor. Recently I got a couple included with a bunch of TV parts, they were set up in just like that. Test it with capacitor checker, or you may find a part number on it, you should be able to figure it out.
I hope so. I think I will.
It's the right color to be one of those little disk-type caps. That was my 1st thought. That it was a multi-cap of some sort. Sort of like a disk version of a cap can?
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Here's a picture with the application sheet, I'm sure yours is a little different but probably similar:
(https://lh6.googleusercontent.com/-bXsz8qP8Dv4/U-Ls2gcx_bI/AAAAAAAAO9k/Ve0oTa47yEc/s640/IMGP2834.jpg)
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It's a resistor/capacitor pack. They were very popular during the '60s for consumer electronics. They ain't all the same. But does it really matter what's inside yours? Don't you plan to replace that tube with a 6SL7 dual triode and build a totally different circuit?
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It's a resistor/capacitor pack. They were very popular during the '60s for consumer electronics. They ain't all the same. But does it really matter what's inside yours? Don't you plan to replace that tube with a 6SL7 dual triode and build a totally different circuit?
Yes, that's the plan.
So I guess I don't need to worry about any of the functions it performs.
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Here's a picture with the application sheet, I'm sure yours is a little different but probably similar:
(https://lh6.googleusercontent.com/-bXsz8qP8Dv4/U-Ls2gcx_bI/AAAAAAAAO9k/Ve0oTa47yEc/s640/IMGP2834.jpg)
Well it looks almost exactly like that. Yeah, it probably has different values than this one but that's definitely the idea.
Slukey makes an excellent point but it's still good to know what it is/was.
thanks.
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I have a question that's sort of related but not exactly. Anyway, here goes...
On a champ turret board the 1st 2 filter caps have the grounds tied together but the 3rd one is grounded separately from those 1st two.
Why aren't the 3 filter caps tied together on the neg side?
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I removed all of the wires from the V1 socket and am I ever frustrated! The person who put it together was fond of wrapping the wire around the lug 2 or 3 times in addition to going thru the lug with it. Wow. It really makes it a pain to disassemble. :BangHead:
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I removed all of the wires from the V1 socket and am I ever frustrated! The person who put it together was fond of wrapping the wire around the lug 2 or 3 times in addition to going thru the lug with it. Wow. It really makes it a pain to disassemble. :BangHead:
yyup. a small flat-blade screw driver is helpful to pry the wire off the lug while the solder is hot... snip... heat,, suck, heat, pry, snip...
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I removed all of the wires from the V1 socket and am I ever frustrated! The person who put it together was fond of wrapping the wire around the lug 2 or 3 times in addition to going thru the lug with it. Wow. It really makes it a pain to disassemble. :BangHead:
yyup. a small flat-blade screw driver is helpful to pry the wire off the lug while the solder is hot... snip... heat,, suck, heat, pry, snip...
i use an x-acto knife and soldapullit, and of course, small cutter and needle-nose pliers. on octal sockets you can heat and flick the terminal with your iron and the solder splatters off: mind your eyes and face (wear safety goggles hombre!). kind of messy but effective.
soldapullit (http://www.edsyn.com/product/DS017.html)
GZ, have you decided what's going in for a preamp?
--pete
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On a champ turret board the 1st 2 filter caps have the grounds tied together but the 3rd one is grounded separately from those 1st two.
Why aren't the 3 filter caps tied together on the neg side?
The first two caps supply the power tube plate and screen. They are considered the 'power' ground.
The third cap feeds the preamp tube and is considered the 'preamp' ground. It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.
Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.
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just doodling... based on princeton 5F2-A preamp. drawing generated with visio 2010. if you'd like to have it in native visio format, PM an email address.
hoping others here will help check for errors. :icon_biggrin:
happy rosin smokin'.
--pete
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On a champ turret board the 1st 2 filter caps have the grounds tied together but the 3rd one is grounded separately from those 1st two.
Why aren't the 3 filter caps tied together on the neg side?
The first two caps supply the power tube plate and screen. They are considered the 'power' ground.
The third cap feeds the preamp tube and is considered the 'preamp' ground. It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.
Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.
Wow! I really can't get my head around how they're separate, when they ultimately go to the same PT post an inch away.
I do get that the 1st two are power and the 3rd is pre tho.
Thanks for the explanation.
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OK so I might have exaggerated a bit in my frustration with cleaning up that socket but the really thin wire from that weird wafer thingy and the almost as thin hookup wire they used were stuck thru the lug, plus wrapped once. So when there were more than 1 in a lug is seemed like it was wrapped around it forever.
I gotta remember the flick-trick.
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Lol... that's old school wiring technique, coming from (I believe) the military. The idea was that even if the solder joint broke completely, you at least had intermittent contact at the wire/component junction, and that would keep the plane from falling out of the sky. As you run into more often it gets easier to desolder.
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Lol... that's old school wiring technique, coming from (I believe) the military. The idea was that even if the solder joint broke completely, you at least had intermittent contact at the wire/component junction, and that would keep the plane from falling out of the sky. As you run into more often it gets easier to desolder.
when I wired homes I was taught to make a good mechanical connection with wires, then put a wire nut on it. So in a j-box we'd always twist any connections with a lineman's pliers then trim and cap it. But we weren't using any solder. But I suppose if it kept the plane in the air it made sense.
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On a champ turret board the 1st 2 filter caps have the grounds tied together but the 3rd one is grounded separately from those 1st two.
Why aren't the 3 filter caps tied together on the neg side?
The first two caps supply the power tube plate and screen. They are considered the 'power' ground.
The third cap feeds the preamp tube and is considered the 'preamp' ground. It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.
Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.
That theory goes by the wayside when using a cap can tho, right?
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It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.
Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.
It's about keeping the B+ 'loop' current isolated then you run 1 'loop' to the next 'loop'.
Here's a few drawings that may help. (G*1 = ground star #)
Brad :icon_biggrin:
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It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.
Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.
It's about keeping the B+ 'loop' current isolated then you run 1 'loop' to the next 'loop'.
Here's a few drawings that may help.
I was looking at the drawings, when all of a sudden they disappeared. I closed and reopened the browser and they're just not there anymore.
?!?
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Sorry I reposted them.
Brad :laugh:
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That theory goes by the wayside when using a cap can tho, right?
Maybe, maybe not.
If you use a dual 50uF cap can and use 1 section for the power tube B+ plate supply and the 2nd section for the power tube B+ screen supply then no.
Brad :icon_biggrin:
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Here's a link to a very good grounding explanation;
http://www.valvewizard.co.uk/Grounding.html (http://www.valvewizard.co.uk/Grounding.html)
Brad :icon_biggrin:
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thanks for the link Brad.
Looks like valve wizard has all sorts of good inf on that site.
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On a champ turret board the 1st 2 filter caps have the grounds tied together but the 3rd one is grounded separately from those 1st two.
Why aren't the 3 filter caps tied together on the neg side?
The first two caps supply the power tube plate and screen. They are considered the 'power' ground.
The third cap feeds the preamp tube and is considered the 'preamp' ground. It's good practice to keep the two separated so the preamp current does not flow thru the same path as the high current power ground.
Those two grounds are electrically connected together thru the chassis, but the currents flowing thru each ground circuit is kept separate.
That theory goes by the wayside when using a cap can tho, right?
it does.
--pete
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just doodling... based on princeton 5F2-A preamp. drawing generated with visio 2010. if you'd like to have it in native visio format, PM an email address.
hoping others here will help check for errors. :icon_biggrin:
happy rosin smokin'.
--pete
Holy cow! That Visio drawing is just what Jane and the monkey said I'd be needing to get this done and they were right.
"Tanks, tanks, and ever tanks"
-Max Calvada
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you're welcome. check it for errors.
--pete
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> I really can't get my head around how they're separate, when they ultimately go to the same PT post an inch away.
Remember we don't have clean power, we get the peaks of 50/60 Hz wall power.
So the PT-Rectifier-main Cap loop is FULL of BIG buzz. Jackhammer racket.
Illustrative digression:
My father says when he was young there was a Juke Joint dance-hall far outside of town (where the sheriff didn't go). Converted from a chicken shack. Skinny floor beams. When the joint got jumping, the floor would bounce up and down six inches.
Now say you see all these customers and want to open a tattoo parlor there. Do you set up....
1) middle of dance floor?
2) shack hanging from the edge of the dance floor?
3) new shack on new blocks a foot outside the dance hall?
With #1 you will be tattooing places the customer doesn't want tatted. Even #2 will foil good workmanship. If I was the artist (and especially if I was the customer!), I'd want to haul in new blocks and be well outside the bounce zone. On the same ground, but not on the same blocks and beams.
In the diagram below, note the jackhammer pulse-path through rect and main cap, and the smooth current through the stage taking your sweet (but weak) guitar input signal. They do connect, but not so the input stage gets the full brunt of the wall-power system.
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LOL!
If you don't teach this stuff (outside of this board) you really should. You have a knack for making it fun as well as understandable. The mark of an exceptional teacher.
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Well I made a little progress today. It looks a lot grungier and more ham handed in the picture than it does in person.
It also doesn't look like a lot of progress but I'm partially disabled and can only do a little at a time before pain tells me it's time to quit for a while.
Anyway, here's what I have so far...
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Looks good to me!
Brad :icon_biggrin:
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Thanks Brad.
Next time I'll try & finish the preamp socket and do the pots.
A 220k resistor is still needed from stock. I'll have to go thru my stuff & find one.
I have everything else. The tube (6sl7) I ordered arrived yesterday along with the Jensen P69R so as soon as I can finish up I'll be able to fire it up.
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The tube (6sl7) I ordered arrived yesterday along with the Jensen P69R so as soon as I can finish up I'll be able to fire it up.
:blob8:
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I have to say that the really nifty color layout that Pete made up really made the difference on this for me.
Thanks a bunch to DummyLoad for his help.
Connecting the resistors and caps right to the tube socket makes their function clearer in mind as opposed to making up a turret board and connecting everything that way.
I only hope I can go long enough on this next leg to get the thing done. Either way, I'll post my progress
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Well, I've finally got it close to being done. No pics just now, but if you guys really want 'em I'll snap a couple & post 'em later.
I'm just fixin' to smoke test it now. Maybe a poor choice of words? So, I was gonna power it on w/o tubes first, then put the tubes in and see if it actually passes a signal & works correctly.
Any other initial power on suggestions would be much appreciated. I'll wait a while & see if there are any replies. The guy across the street is a harp player & tomorrow night is his band's practice night so if all goes well before then, I think I'll have him put it thru the paces for me. He's playing one of my Champ clone builds now. Has been for the past year & loves it. I'm really interested in hearing this one in an "A-B" comparison test with that one. This will be my fist experience with an octal preamp tube.
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It was a bit of a blivot but here it is.
A blivot is 10 pounds of s**t in a 5 pound bag. It's what my mother used to threaten to give us for Christmas back in the day...
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The good news is...no flames, smoke, or tripped breakers.
The bad news...no sound. Nuthin. A barely audible hum....if that.
Back to the drawing board I guess...
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possible short? see pic.
--pete
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Good eye!
I'll have a look & let you know.
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Wow! That was an amazing piece of spotting the/an issue from a distance man! That was a great call Pete.
Only now I have something else going on. As it warmed up it began feeding back and the FB just got louder and nastier as it got warmer.
I pulled the plug right away because I didn't want to fry something. I can't fiddle with it anymore tonight, but tomorrow I'm going to have to try & figure this out.
Any ideas?
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It looks really good to me!
You'll find what's wrong.
And Yes Pete's very good at drawings and coming up with mods to amp builds isn't he? He's helped many members here through the years, me included! :icon_biggrin:
Wow! That was an amazing piece of spotting the/an issue from a distance man! That was a great call Pete.
Must be that good fresh Texas air and sunshine that makes his eyes so good. :huh: hehehe
Brad :icon_biggrin:
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I'm positive I never would've gotten this far if it hadn't been for his Visio drawing and other help. Not to mention the rest of the help I got from this bb.
So for the record, as it warmed up it started making a high pitched, steady, feedback sort of noise. Not a screech but just like a mic too close to a speaker sort of noise that got louder and louder 'til I killed it.
Actually, it's probably a good sign. If I can get this runaway FB under control, it sounds like it's gonna be just as loud as my 5F1 builds.
That, after all, was the point of this entire exercise, right?
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does it feedback when both controls are at "0"?
aside from a wiring error - things to ponder:
1) the 250k resistor that hangs off of pin 5 of the 6V6: is it grounded on the input jack?
2) if yes, then move the 250K to pin 5 of 6V6 ground end: ground it on the 6V6 socket.
3) the input jack may be too close to the 6V6: rotate the input jack so that the tip lug is closest to pin 1 of the 6SL7 and make that wire as short as possible.
--pete
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That resistor is grounded on the socket lug. it goes from pin 5 on the 6v6 right to the ground lug below it on the 6v6 "frame".
Tomorrow, I'll try moving the input jack and let you know. That wire is only about an inch long now but if it can be shortened any, I will.
If you can think of anything else, Please feel free to let me know. For example, if you can think of what kind of wiring error could cause this symptom.
Thanks again and again, and I'll report back tomorrow.
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Oh...maybe you saw that black ground wire on the input jack & thought it was the 6v6 pin 5 resistor?
That ground wire does go to one of the tube socket ground lugs. i don't recall which one I soldered it to.
Should I move it?
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It looks really good to me!
You'll find what's wrong.
And Yes Pete's very good at drawings and coming up with mods to amp builds isn't he? He's helped many members here through the years, me included! :icon_biggrin:
Wow! That was an amazing piece of spotting the/an issue from a distance man! That was a great call Pete.
Must be that good fresh Texas air and sunshine that makes his eyes so good. :huh: hehehe
Brad :icon_biggrin:
thank you for the kind words...
it's the heat. that unbearable 100 degree humid heat. :icon_biggrin:
--pete
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it's the heat. that unbearable 100 degree humid heat. :icon_biggrin:
NO, it's not the heat Pete (hehehe), your a good man and it's been proven MANY times here by how much you've contributed here to all of us, just a tip of the hat to you. :wink:
Now back to our regular programing.......... and a 1 and a 2....... 'Do the hip shake thang', a do the hip shake thang', a do the Texas Zydeco hip hip shake thang.......
Brad :m2
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it's the heat. that unbearable 100 degree humid heat. :icon_biggrin:
NO, it's not the heat Pete (hehehe), your a good man and it's been proven MANY times here by how much you've contributed here to all of us, just a tip of the hat to you. :wink:
Now back to our regular programing.......... and a 1 and a 2....... 'Do the hip shake thang', a do the hip shake thang', a do the Texas Zydeco hip hip shake thang.......
Brad :m2
LMAO! :l2:
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Upon doing a search for feedback problems I ran across this..
Some causes of squeal...
- Tube going microphonic - most often first preamp tubes.
- Shorting contact on input jack (esp #1) not making contact; the "squeal" is from sound vibrations vibrating the chassis and the contact making and breaking contact repeatedly, making a little 'click' each time.
- Power tube shorted (this only happens for a short time - the amp squeals and then dies.)
- Lead dress - the leads carrying the signal around inside the amp have been moved around somehow so that the signal is causing internal electrical feedback. You can find this by running the amp with the chassis open and moving the wires around (gently! with a wooden stick) to see if the squeal changes or goes away. Once you locate the critical wire(s) you can figure out where they have to be to keep this from happening and tie them there. Another option can be to substituted shielded wire for the sensitive ones, with the shield connected at one end of the run only.
- If the amp has been modified, the squeal may be caused by poor lead dress in the modification, improper grounding in the modification, parts layout too close, or just that the new (usually higher) gain has pushed things over the edge. Higher gain makes a lot of things more critical, including grounding, bypassing, lead dress, and signal shielding.
- Wrong polarity/ incorrect hookup of a replacement output transformer.
I bought two used 6sl7s so I can try swapping the one that's in there for the other one.
I didn't hear any clicks but #2 could be it I guess.
#3 scares me the most since they don't specify the cause of death. I'll check & re-check my work & hope I don't fry anything. Before I found the short that Pete pointed out, it was powered on for a few minutes not making any sound. So if the 6v6 was in fact shorted, wouldn't it have failed catastrophically? Or did that short at pin 5 of the 6sl7 somehow prevent it from going up in smoke? Again, I wish they'd have said in what way it dies.
#4&5 are similar and could be the problem. It's the blivot syndrome.
I don't see how it could be #6 since I didn't change that.
So I guess I have my work cut out for me. I don't wanna cook anything in the process. Tips are encouraged at this point.
Please and thanks guys!
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Well, just to update this thread, I did wade back into the amp yesterday and found that I had misplaced one of the connections on the volume pot. Pete was also of the opinion that the input jack might be too close to the 6V6 so I fixed that too. I wasn't really pleased with the way that little piece of shielded wire turned out either so I redid that as well. I took a forceps and generally tried to tidy things up too. The amp works but I have 2 6SL7s that I bought used and both are micro-phonic. It amplifies the sound of any jostling or tapping of the cabinet, and pings like a wine glass if you so much as touch the 6SL7. Plus it seems untable since it wants to try and squawk a little intermittently. Pete tells me that's an indication of "one or more of the grid wires in the grid element is sagging and touching another." So I can't really report on what it sounds like until I can get that issue resolved and test again. However, it the mean time, Here's the latest looksee.
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as it warmed up it started making a high pitched, steady, feedback sort of noise.
That's a drag about the 2 6SL7's but it's not doing the above any more, that's good.
Brad :icon_biggrin:
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Yeah, I thought that I was hedging by buying 2 of 'em. One is decidedly worse than the other but they're both totally unacceptable in the amount of microphony. I didn't want to buy any current production 6SL7s because I've heard too many bad things about them and NOS are just too darned expensive. I suppose I'll have to go with one or the other though. I have a friend with boxes of that kind of stuff. Maybe I can find a good one there and make a swap or something.
It still feeds back at high volume, but couldn't that be another function of the microphonic tube? I mean, with a good tube, maybe it'll settle down?
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OK. I got some more 6SL7s and boy do they make the difference! That little amp sounds pretty darned good. It's very close to being there except for one more thing.
At full volume and with the tone control turned all the way to bass, it just barely keeps from feeding back with no input, and then when you turn the tone control towards treble, it starts motor boating.
In doing a search for motor boating I've seen it blamed on too much gain, and on filter caps just for a couple of possible causes.
So what do you guys think?
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Does anyone have an opinion on changing that 220-ohm cathode resistor on the 6V6 to a 470-ohm like a tweed champ?
Going that direction with the value of that resistor will do what?
If I do that, will I also need to change anything else?
Please & thanx as always.
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Increasing the value of that resistor will decrease power out and let the 6V6 run cooler. You should not have to change anything else.
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Thanks Sluckey!! :worthy1:
I'm trying to dial this thing in to where it doesn't want to feedback when dimed, like my tweed & bf champs
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Well, it's finally working and WOW...is it ever a killer!
After the initial mods it was still not right. It was motor boating as the volume control went beyond about halfway. Sort of blub, blub blub noise. The B+ at the 6V6 was off a little so a resistor adjustment corrected that.
That motor boating was persistent even after making sure the voltages were all correct. It only became more defined and rather than blub, blub, it started making an articulate sounding putt, putt, putt.
Pete gave it some thought and determined that the "C" tap from the cap can was bad. This was the power supply filtering for the 6SL7 and so he helped me to make the necessary changes to add one 8uF 450v cap (cuz it's what I had handy) and BINGO! It sounds great!
It gets just as loud as any 5F1 clone that I've built, with maybe a little less clean headroom but hey..who needs a bunch of amps that all sound identical? The distortion at full volume is fantastic! Think Led Zepellin's Moby Dick. Just my Les Paul with DiMarzio humburckers and nothing else.
I'm not thrilled with the tone control as it gets harsh very quickly as you roll it from bass to treble but I think I leave it alone for now.
I have to find a way to extend the pot shafts yet but that's minor. The little amp's a real sleeper. You can crank it and rattle the windows. Didn't take long for Jane and the monkey to start complaining. I'll have to hook it up to a couple of different speakers to see how the old Jensen AlNiCo 6X9 compares to say a Weber 8F150.
Thanks again to Pete and all of you guys who contributed ideas. I learned a lot from this project.
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All right!!!!! :blob8:
Didn't take long for Jane and the monkey to start complaining.
Send them out to get some bananas. :laugh:
Brad :icon_biggrin:
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Looking back, I see that I never offered up any pictures of the thing in it's entirety. So...here it is..
I swapped out that speaker with an old Jensen AlNiCo I had, in addition to the other mods.
Ain't it cute?
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nice looking little thang. glad you're happy with the mods.
--pete
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I really like this kind of project. Thanks for sharing.
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schematics of what was built.
hope you're diggin' on the new groove...shock the monkey.
--pete
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I read Tone Quest Report mag (have all the back issues) and they had a couple of interviews with west coat blues guitar players who LOVED oval speakers as a sleeper for mojo sound.
Those guys searched under every rock, once they stumbled across them in old pawn shop buys and bought every one they could find. :dontknow:
I've been spending hours, literally searching for the last year for amp cab coverings and grill cloth to get away from the normal tradition in color schem. :BangHead: :cussing:
The tolex on it looks great, the depth of grain and the depth of color!!!!! The cab it's in looks way cool all the way around, I love it!!!!!! Plus the cab locks!!!!!
Brad :icon_biggrin:
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Thanks once again to Pete for the schemo! I can put the as-built in the box alsong with the original for some future tube guy. If there ever is such a thing as a future tube guy. :sad:
I'll been on "Large item collection day", if your town's trash collection offers one, you could find old TVs and consoles on the curb for the picking. Old speaker and tube chassis heaven! A wire cutter and set of nut drivers is prolly all you'd have to carry.
I've tried looking for that Silvertone style of tolex with no luck at all. I think some of the old tolex, y'know, the really unusual stuff might be best approximated with wallpaper. You might find something that'll meet your needs at home improvement place or, if you're lucky enough to have a very old decorator in your town, 3rd ot 4th generation or even older, they may have really old out of print stuff that could be used to cover a cab. Old radio guys often have grill cloth that's different from the usual oxbloody tweedy stuff that's so popular right now. I'll bet there are other sources too if one thinks outside the box as they say. I think the trick is to find a cloth that's sonically transparant. I read in one of the forums that a guy improved the sound of his reissue champ 600 by replacing the grill cloth. It seems the stuff they put on that thing in the factory could make pretty good soundproofing if used in a couple of layers. I don't know this to be fact but it seemed like the thread had some creedance. I'll bet an upholstery shop would be a good place to hunt for unusual cab covering and grill cloth too.
BTW and FWIW
I've found that the old radio people aren't nearly as high priced as the old tube amp people when it comes to selling parts and stuff. I've seen some really interesting and unusual old radio cabinets on flea bay with asking prices that way below what a run of the mill 5F1 cab goes for. With a little imagination I think one might use all of the exsisting openings in one of those and make a cool little combo out of it. If you had to do any surgery on it, obvously it would get a lot trickier and then you're back to trying to find an appropriate covering mat'l.
Anyway, that's been my experience to date.
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The monkey was surfing schematics and found these:
http://www.oldfrets.com/Valco/Schematics.html (http://www.oldfrets.com/Valco/Schematics.html)
And there, he found this:
http://www.oldfrets.com/Valco/Schematics/1950SuproSpectator.jpg (http://www.oldfrets.com/Valco/Schematics/1950SuproSpectator.jpg)
And then he came up with a couple of questions. He says he noticed that the Spectator didn't seem to have a cathode bypass cap on the 6V6, (Or so he says...we're dealin' with a monkey here.) and if that's the case, what effect does that cap have anyway?
It also appears to be minus on cap on the (second stage?) of the 6SL7.
What's up with that?
The monkey thanks you for your input in advance. He's thinking of building another version of my Newcomb from scratch in a blank chassis box using some ClassicTone transformers he has laying around and is wondering what the differences are between what I have and what the Valco version is.
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Valco built a lot of cheap stuff. The missing caps were probably a cost cutter. Installing cathode bypass caps will increase the gain and also make the amp sound more bassy. The cheap speaker that was in that amp probably could not handle the extra bass response, so just drop the caps from the circuit too. No one will ever know. We'll market it at Monkey Wards or Western Auto for $49.99 regular price.
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Valco built a lot of cheap stuff. The missing caps were probably a cost cutter. Installing cathode bypass caps will increase the gain and also make the amp sound more bassy. The cheap speaker that was in that amp probably could not handle the extra bass response, so just drop the caps from the circuit too. No one will ever know. We'll market it at Monkey Wards or Western Auto for $49.99 regular price.
LOL :l2:
Actually he went to Jane 1st. She told him to ask me and since he seems to notice stuff like that before I do, I figure he's already ahead of me on it.
So I put it to you guys. He wonders because he's heard that these Valcos are often prized by harp players. In addition to singing boogie-woogie, he's thinking of taking up the harp. Jane's already screaming "Shut up baby I'm trying to sing!!" every time he open's his mouth so I have no idea what he thinks he's gonna gain by trying to blow a harp.. :dontknow:
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We need to hear it straight from the Monkey. What does the Monkey really think?
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Back at the point where I mentioned that I needed to extend the pot shafts I sorta figured someone would say "DUH!, that's an easy one" and clue me in.
I'm still betting you guys have all sorts of ways for doing that and I'm fairly certain I'm not the first to think of this one. Still, I think it was a pretty decent idea I had this morning so I thought I'd share it. It wasn't the rods that I was stumped on but the couplings...
It suddenly occurred to me that guitar tuner bushings might just do the trick. So I went to my boxes of miscellany and found some plastic ones and they're perfect!
Just trim off the flange and they're like that was what they were made for.
The shafts from old unwanted or bad pots can make the extension or any hunk of 1/4" OD dowel or metal rods completes the deal.
I don't know if I'd try and use this method if you had to extend 6" or something like that, but I only needed to go about 3/8" to make up for the thickness of the wood cabinet and for that, this was just right. The right price too.
:wink:
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1/4" couplers are very common. I got these on eBay for cheap. AL rods from Lowes.
(http://home.comcast.net/~seluckey/amps/RCA/RCA_17.jpg)
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if you don't need them as long as steve's, the PEC brand of pots are available with 2" shafts. NTE also sources PEC pots, however, digi-key is the best source. PEC pots are expensive usually $8.00 or more depending on supplier. NTE packaged PEC pots are higher than a cat's ass, but they're available.
http://www.nteinc.com/pot_web/pdf/KU_series.pdf (http://www.nteinc.com/pot_web/pdf/KU_series.pdf)
--pete
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I knew that long shaft pots were available but I elected to go with what I had on hand. The knobs that the amp came with had the sort of hubs that kind of stick out past the skirt, if you can picture what I mean. So the short shafts weren't a problem for the original parts, but the hubs were mismatched, cracked and loose. I just figured on getting a couple of knobs like the ones it came with but then I was surprised to find out that they're not as common as I assumed they were. If I'd realized all of that before I soldered it all together I would have ordered a couple of pots with long shafts. Heck, I had all sorts of time. I fiddled around with that thing for days before I got to the pots. So, live and learn right? If I ever run into this situation again I will order the correct pots right off the bat.
Another thing I didn't do was to try the hardware store. I suppose one could find some thin walled, rigid 1/4" ID tubing in brass, aluminum, or any number of materials. I just don't get out much anymore and being on my feet for an extended period of time is literally a pain in the piriformis. So browsing a big box type of hardware store is pretty much out. Maybe a hobby shop. I can't imagine a piece of tubing being more than a few bucks and if you had a foot of the stuff you'd be set for at least a dozen extensions. Probably more.
I did try searching eBay for those couplings but everything I found looked like it way too thick.
Funny how the things that you figure will be cheap and simple turn out to be the ones that are the hardest to solve solve sometimes. The tuner bushings worked great in a pinch and someone working on a guitar amp might be likely to have those kind of odd parts sailing around like I did. So I thought I'd toss it out there in case anyone found themselves stuck.
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> guitar tuner bushings might just do the trick
Sweet!
My go-to was always 1/4" rubber fuel-line. Pretty snug fit on traditional pot shafts. True, it will slip if you jam the knob past 10. But you just turn the other way to zero, and it's cool until you force it again.
I suppose if you forced it a lot, you could use hose-clamps. But that's more money and trouble.
Car-parts store. No walking-around (know what you mean about big concrete box-stores), you just say "a foot of 1/4" fuel line" and the counterperson cuts it for you. You hardly have time to pick up some fuzzy dice and some fine sandpaper.
The rubber may be useful in some settings. Steve's chassis may be an old radio, chassis deep inside a decorative wood cabinet. Old wood warps and twists. The holes in the wood could get out of line with the pots. With rubber coupling you could bush the shaft in the wood, then run a 2 degree flex in the coupling to the pot.
Much more elaborate couplings used to be common. Flex joints. U-joints. Some radio chassis have to put the tuning-cap in catty-corner to get the leads short, and U-joint the shaft to the front. There were even cables (like speedometer cables) where you have the knobs on the dash and the radio under the seat or under the floor. A lot of that stuff has vanished in this day of digital everything.
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WOW! Hooda thunk? Spedo cables! I suppose some creative engineering had to be employed in the radio-under-the-seat days.
Fuel line sounds perfect. Friction fit like push on knobs but less likely to crack.
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does anyone recognize this?
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I recognize the file names. :icon_biggrin:
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That's the amp you just rebuilt?
Brad :think1:
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No it's not the Newcomb. I have my eye on this as a possible for the suitcase amp. It's all octal, and the right size. 10 X 5 X 3. The tubes are 1-ea 6SN7, 6SJ7, 7Y4, and unkown.
I'll have to drill new holes for pots, pilot, & input(s) on one long side as the pot-on-the-end config won't do for this project. But that's not too bad. At least I don't have to drill everything as in a new blank box. The seller dosn't know what it is and I was hoping maybe someone here with vastly more experience than I might recognize it. If someone did happen to ID it for me, I could start hunting a schemo for it & start trying to figure out how to proceed should I end up with it.
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I was just wondering if it would be safe to sub a 6SN7 for the 6SL7 in the Newcomb just for the sake of experimentation. Also, are there any other tubes that can be subbed for the 6SL7?
I'm curious since there are so many 12AX7-types that can safely be swapped for an actual 12AX7 and wondered if the 6SL7 has a similar set up. Also, are there any other power tubes that can safely be swapped for the 6V6? I just wanted to experiment a bit but not if I have to go under the hood to do it.
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Here's a thread on 6sl7 vs 6sn7: http://alt.guitar.amps.narkive.com/cIdXB4fd/6sl7-6sn7-vs-5691-in-a-49-princeton (http://alt.guitar.amps.narkive.com/cIdXB4fd/6sl7-6sn7-vs-5691-in-a-49-princeton)
I've had good luck with 5881 instead of 6V6 in a BF Deluxe Reverb (with bias vari tremolo), you'll have to adjust your bias of course.
Is your PT beefy enough?
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I'm not sure about the PT. It's physically very small. Smaller than, oh, say a champ tranny but then it doesn't have the 5v windings. Minimal markings and what's there appears to be an oem number which matches part number on the (original) schematic. When I was still shooting trouble on the mods I did to it, I checked voltages and cam up with the following:
6SL7
Pin 2 = 162
Pin 3 = 1.4
Pin 5 = 159
Pin 6 = 1.5
6V6
Pin 3 = 319
Pin 4 = 267
Pin 8 = 11.7
if that helps any.
The PT seems to run cool tho. Does a 6SN7 make the PT work harder than a 6SL7 does?
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6SN7 has twice the heater draw of the 6SL7, so that would be a definite yes. Give it a try, but watch your PT temps.