Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: scstill on December 11, 2022, 03:57:13 pm
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I'm thinking the shortest heater wire the better.
So on these old time flat sockets I just ran across the center to the next socket
Is this ok? or should I lengthen and run out of the way in the side creases of the cabinet?
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:huh:
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(https://i.imgur.com/McSPugj.jpg)
Franco
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If I was gonna wire them like that I'd fly them about 1" above the sockets (Fender style). I put mine in the back crease of the chassis, but all my tubes were lined up across the back which made it easy to do so.
If I had to do it again, I would replace those crappy wafer sockets. They have been a PITA. I knew they would be. But would I listen? Oh no! Every time I pull out my old RCA radio conversion I have to spend ten minutes wiggling tubes around so they make good connection again. :BangHead: :cussing:
Here's mine...
http://sluckeyamps.com/RCA/RCA_07.JPG
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Too close to socket pins, you can burn these wire when soldering resistors, capacitors and wires to pins
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Kagliostro's and Sluckey's examples are gorgeous. One thing to note on Stuckey's photo is that he has not twisted the heater pair -- just tucked them well out of the way (and I bet there is no heater noise!).
The main thing you want to do is avoid have signal wires running parallel with noisy wires -- and, if your signal wire must cross a problem wire, do so at a right angle. Of course, all this is most critical in your early preamp stages . . .
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Brand as Geloso near always feeded V1 or all preamp tubes with DC
However you can go AC, thousands of tube amps has filaments in AC
I think that with a bit of effort you can rotate those sockets to have filament PIN positioned in a better way to advantage your heater wires path
Franco
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If I was gonna wire them like that I'd fly them about 1" above the sockets (Fender style). I put mine in the back crease of the chassis, but all my tubes were lined up across the back which made it easy to do so.
If I had to do it again, I would replace those crappy wafer sockets. They have been a PITA.
In the revision (below), they fly above the 6v #84/6z4 rectifier and get buried in chassis for the other tubes.
There is a 100ohm artificial CT at the start and a LED at the end (goes into a cabinet hole).
Hope I don't regret not replacing wafers. Is there a good place to source 4, 5 , 6 pin sockets?
Too close to socket pins, you can burn these wire when soldering resistors, capacitors and wires to pins
I started using hi temp silicone wire some years ago after frustration melting insulation.
Might be moving to cloth push back as that seems to be trending here.
Does anyone know where to source coax that has center insulation in silicone?
I'm still melting the coax sometimes....
Kagliostro's and Sluckey's examples are gorgeous.
Yes!! definitely agree their's are gorgeous. And their board work is also beautiful.
There are so many builders in this forum that do exceptional work. Much eye candy...
I have not done a circuit board build yet. Still hand wired point to point.
More difficult to change parts but very gratifying figuring out the layout (every build is different challenge)
BTW - this build (in a Philco 926) has that "RatRod" look (below). It will never be gorgeous with so much clear coated rust
Brand as Geloso near always feeded V1 or all preamp tubes with DC
However you can go AC, thousands of tube amps has filaments in AC
I think that with a bit of effort you can rotate those sockets to have filament PIN positioned in a better way to advantage your heater wires path
Thanks for the Geloso reference. They are pretty cool. Maybe I'll find one someday.
You are correct, when this build was a radio, heaters were 6vdc.
This guy will have AC heaters.
Below are a few pics of this build, Including the new heater route.
It was a Philco 926 radio and someone had labelled it with a "36 Pl" on the front.
No idea what it means, '36 Plymouth, '36 Philco??
Since it was kept under the clear coat, I decided to name this guy "Phirty6", a play on Philco and 36. This goofy name is also somewhat in its timeframe as the original schematic is dated 1938 in the John F Rider book.
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Haha. I didn't look very closely at your sockets. Better just clean those up, do a little tightening and use them.
I use RG-316 coax. The center is teflon insulated and even the outer jacket is made of some kind of heat resistant material. Only about 1/8" diameter. No more melted insulation. You can see some in that rca pic I posted. Buy it on eBay.
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Haha. I didn't look very closely at your sockets. Better just clean those up, do a little tightening and use them.
This is my first time with tubes this ancient. Very excited.
Uses an 84 rectifier and a common 41, The two channel lineup will be:
Ch1: 78(as triode) - 75 - 41(SE)
Ch2: 78(as pentode) - 6A7(as triode??) - 41(SE)
Tube evolution is 58-78-6Sk7; 75-6SQ7; 41-6K6
Will be low gain, but this could have some low volume cool tone. We'll see
My plan is to use a three position channel switch with single input jack
up - triode channel; down - pentode channel; middle - both
any obvious issues with this approach?
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My plan is to use a three position channel switch with single input jack
up - triode channel; down - pentode channel; middle - both
any obvious issues with this approach?
A special toggle switch (C&K-7211, ON-ON-ON) makes this easy. But you need to consider the rest of the circuit to know if there will be any phase cancellation when you mix the preamps together. Looks like you are planning on three inverting stages in each preamp so you should be good.
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A special toggle switch (C&K-7211, ON-ON-ON) makes this easy. But you need to consider the rest of the circuit to know if there will be any phase cancellation when you mix the preamps together. Looks like you are planning on three inverting stages in each preamp so you should be good.
Yes that is exactly the type of switch planned for.
I've used this switch many times to get multiple speaker out taps.
Gonna be fun to see it work on the input.
I need to educate myself on the phase cancellation issue.
Because if I'm doing it right it is just dumb luck.
Any suggested references?
I've never operated the 6A7 as a triode (its a pentagrid) and not sure that will be successful
It has many grids and I only want the Input Grid (on the cap).
If not possible, I will combine the two preamps 78's at the second gain (75)
I have done this with another build (with octals) and did not see any issues.
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I need to educate myself on the phase cancellation issue.
Not much to it. Count the number of inverting gain stages in each preamp. ***A CATHODE FOLLOWER IS NOT AN INVERTING STAGE***. If you have an even number in one channel and an odd number in the other channel, you will have phase cancellation at the mixing point.
Here's an example of even and odd inverting stages before the mixing resistors...
https://el34world.com/charts/Schematics/files/Fender/Fender_deluxe_reverb_ab763.pdf
The normal channel has two inverting stages before hitting the 220K mixing resistor.
The vibrato channel has three inverting stages before hitting the 220K mixing resistor.
If you apply the same signal to both channel inputs, that signal will get inverted twice in the normal channel and it will get inverted thrice in the vibrato channel. IOW the two signals will be 180° out of phase when they are mixed (summed) together and they will tend to cancel (subtract) each other. It is rarely a perfect cancellation but the results is a thin sounding (non musical) tone.
Now if the channel signals arrive at the mixing resistors they will be additive, reinforcing each other and the results will be a fuller, pleasing sound.
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Thanks, very good explanation.
Kind of why we phase invert Push Pull before applying signal to the OT.
I often like to patch channels and two jacks per channel tends to imply patching,
but with this classic design you can not do that, in fact if you do it breaks it (thin sound)
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Just double checking
Is it acceptable to run HV along the heater route?\
Or better elsewhere?
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I would keep it an 1" above. if you can try and put the PS RC filters (taps) close to intended tube, that helps "breakup" long runs of DC running parallel to AC
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... Is it acceptable to run HV along the heater route?
Or better elsewhere?
I built an amp with a preamp chassis connected by umbilical to a power amp chassis. I was concerned that running the heater & B+ power in the same multi-conductor cable might cause problems.
Turns out, no problem in my case. They probably ran closer-together, over a longer distance, than what you're contemplating.
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Thanks
This was purely an aesthetic consideration; thinking the HV would look better tucked out of the way.
But since there might be a functional issue, decided to run separately.
Looks ok too. OT is on other side where the red wire exits top left
You helped me recall another project in waiting.
Split chassis Supro where the upper to lower chassis cable bundle had Signal, heater and HV
It was suggested on this forum to run the Heater and Signal in STP. HV was single wire. Hopefully it will be quiet when I finally plug it in in the not to distant future.
See #25 and related here https://el34world.com/Forum/index.php?topic=27263.msg313440#msg313440
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thanks