Shielded Wire Confusion

[kd]

I've read a number of threads concerning shielded wire and now I'm confused. I've got the white Apex teflon wire but in one thread it said this isn't the correct wire due to the low capacitance of the wire. I've seen recommendations for RG59 and RG174 but as far as I know the insulation on this wire doesn't have a voltage rating. I have some 2 conductor foil shielded wire, will this work? I would appreciate any guidance.

Thanks,
Ken

[bluesfendermanblues]

IMO it depends on the amp. If its dark you could go with coax with lower capacitance and vise versa if the amp is brightish.

Judging by the gut shot pictures of dumble amps, he used both types for various amps.

IMLE RG54 is low capacitance, around 20 pf per Ft. Same as thin George L
RG174 is around the double capacitance.

Measure your cables capacitance per ft. And listen to your amp does it need to be darker or brighter.

[David Root]

You are right about the RG wire, it is too low voltage insulation for anything except the input jack to V1A grid according to its spec, (30V max.) but I did in my early days use RG174 and have put +70VAC thru it with no problems. I stopped using it because its conductor is copper plated iron, not solid copper.

I have used the white Apex coax in both 24 and 22 ga, nothing wrong with it from that point of view. I have put close to 200VAC signal on the 24 ga Apex with no problems. Teflon insulation is good!

I believe the comment you are referring to was made by Funk specifically to Dumble circuits, no doubt in relation to the higher capacitance of the "correct" cable smoothing the signal highs a bit.

There's all kinds of ways to do that, easiest might be to change the V1A grid resistor from 22 or 33K to a higher value if the amp sounds a bit shrill. That is a monolithic change ie it affects all circuits following it. OTOH after you have some hours on it it will loosen up and smooth out a bit anyway.....

Truth in Advertizing Dept.--I have ordered some of Funk's cable, which he graciously offered to us, and will check it out and see what the uF/ft is compared with the Apex stuff.

[kd]

Thanks for the replies.

Truth in Advertizing Dept.--I have ordered some of Funk's cable, which he graciously offered to us, and will check it out and see what the uF/ft is compared with the Apex stuff.

I sent him an email on Monday concerning purchasing so of that wire and have not heard back. Maybe I need to use the email address on his website.


Ken

[Max]

I believe the comment you are referring to was made by Funk specifically to Dumble circuits, no doubt in relation to the higher capacitance of the "correct" cable smoothing the signal highs a bit.

There's all kinds of ways to do that, easiest might be to change the V1A grid resistor from 22 or 33K to a higher value if the amp sounds a bit shrill. That is a monolithic change ie it affects all circuits following it. OTOH after you have some hours on it it will loosen up and smooth out a bit anyway.....

As far as I know the effects that different shielded cables have on "tone" is not only due to their capacitance, and that's why you can't get the same effect on "tone" with a capacitor. Our ears are very very fine tuned devices.

And Dumble used very different shielded cables over the time (every ODS generation does have different ones e. g.).

I know of some later "blackface" amps where you find at least five different kinds of shielded cables (diameter, stranded core, solid core, dielectricum, capacitance etc.), and capacitance was sometimes higher then 70pF/ft.

Cheers

Max

[Structo]

Can you explain that a little more in depth?

I understand you can see if there is more than one kind of shielded cable inside an amp if you are lucky enough to get a peek inside.
But, how would you happen to know if the cable is 70pf/ ft or higher?

[Max]

But, how would you happen to know if the cable is 70pf/ ft or higher?

Some Dumbles have reverb and use exactly the same kind of shielded wire for the connections between amp and the tank as is used inside for some of the signal connections. And to measure the reverb cables is easy.

And sometimes he provides cables for the connections between Dumblelator and amp and these are the same as used inside some amps. And sometimes he simply tells people precisely what kind of cables they shall use for the Dumblelator amp connection or the tex-reverb to Dumblelator or the preamp to poweramp connection and so on.

And sometimes you can see the kind of dielectric and if it is solid or stranded core without desoldering the cables. And sometimes you can measure the gauge of the core and the dielectric and the cable without desoldering it and then you can find out what kind it is and then it is not so hard to find a data sheet of this kind of cable.

Cheers

Max

[butwhatif]

There is a lot of shielded wire out there, and I like to stay away from the lo quality stuff, in which one might include tv cable/RG-59 as used in most ods- and i think the primary reason he used it is it's avail in the dumpster as well as a store.
If u own a studio, you've heard the differences a cable can make. Here in DD land we fortunately have choices.

[erwin_ve]

But, how would you happen to know if the cable is 70pf/ ft or higher?

Some Dumbles have reverb and use exactly the same kind of shielded wire for the connections between amp and the tank as is used inside for some of the signal connections. And to measure the reverb cables is easy.

And sometimes he provides cables for the connections between Dumblelator and amp and these are the same as used inside some amps. And sometimes he simply tells people precisely what kind of cables they shall use for the Dumblelator amp connection or the tex-reverb to Dumblelator or the preamp to poweramp connection and so on.

And sometimes you can see the kind of dielectric and if it is solid or stranded core without desoldering the cables. And sometimes you can measure the gauge of the core and the dielectric and the cable without desoldering it and then you can find out what kind it is and then it is not so hard to find a data sheet of this kind of cable.

Cheers

Max

Max; where did you get all that info? Where are you from, have you been close to HAD? Anyway thanks for sharing...

[Aurora]

I've seen recommendations for RG59 and RG174 but as far as I know the insulation on this wire doesn't have a voltage rating.

This is not correct , - RG58,59,174 etc usually have DC limits well aboce 1 kVolt...just find a decent data sheet....

Some years ago, I was building optical photometers, which uses photmultiplier tubes, usually running off som 1000V or more.
I always used RG59 for HV feed cables. 1800 V DC limit....
Never saw a failure for this reason, at least..

[David Root]

RG174 has two grades, UL and non-UL (Military) according to the Belden 8216 spec sheet. UL is max. voltage 30 VRMS, Military is 1100 VRMS!! I think the stuff we get is the 30V rated.

This confounds the issue even more. I stopped using RG174 because it was lo-rated for AC at 30V and because it is a steel core, not copper.

Does anyone have a reconciliation of this spec? Now I'm confused.

[butwhatif]

I have seen the steel core of the coax cables make for add'l hum in a couple instances, because of it's permeability for electromag radiation.

[Aurora]

HMMM- you're right... I guess I've never seen the low grade versions...
should be OK, though, as long as you watch out. OTOH - there is not very much use for a piece of coax to handle the full B+, is there...???

BTW- there's also an RG178, thin low cap teflon core coax rated at 750V RMS... Belden 83265 or Mil M17/169-00001
Even if it is pricey, how many feet do you need for one amp?

[Funkalicousgroove]

If I missed anyones PM I'm sorry, You can email directly info_at_bludotone.com

replace_at_ w/@

it's 30pf/ft 21awg(roughly- it's mil spec)conductor and is rated up to 800V DC

Older amps had Radio Shack "Tandy" RG-59

[kd]

Thanks Funk, I'll be sending an email to order some.

Ken