RVT1K
Super Member
Seeing that HP unit brought back memories of the 3708A that I used back in the mid/late 90's.
Capacitor replacements
- Thread starter kears
- Start date
Seeing that HP unit brought back memories of the 3708A that I used back in the mid/late 90's.
I've never taken any measurements myself, so thanks for sharing yours. Yep, I'm convinced - the inductance is too low to be an issue.
That made me smile. Otherwise, maybe Iceland's volcanos are becoming even more active. That's in a vaguely general direction from my perspective in the US midwest.
AK experts: Because very loud music can approach 50V, at the speaker terminals, would it pay to go higher than 50V working voltage for x-over caps? I realize this is extreme, but for someone who has a big amp and does play at very loud levels, might that oddball benefit from high WV caps?
Any chance you might mind measuring a 1k carbon or metal film resistor, 1/2 watt or so if you've got one handy? Basically any of the modern types that have a spiral cut in the resistive material to set the value. Curious how much inductance they actually have and if its enough to truly make them unsuited for use as grid stoppers in tube gear.
Since you are in Ireland then HiFi Collective in the UK is not all that far away.
They carry a Jantzen CrossCap film cap in 5.1µF and a Jantzen 10µF Elco, these would work just fine for you. I have bought from HFC many times and also used many Jantzen caps, both have proven to be reliable.
https://www.hificollective.co.uk/catalog/001-0252-5-1uF-400v-jantzen-cross-cap.html
https://www.hificollective.co.uk/catalog/jantzen-elecap-electrolytic-cap/001-6135-10uf-100v.html
Don't get too hung up on the cap debates. It is simple maintenance. The chances of 40 year old elcos getting better over time are low.
Cheers,
James
I did an assortment of 8 in various sizes and resistances around 1K - 800 ohms to 1.5K. 1/4W, 1/2W, 1W, tested from 10 KHz to 10 MHz. I did an open and zero cal on the instrument first. A couple of carbon comps in there for comparison.
None (except for one, discussed below) showed any appreciable inductance; any inductance they had was overcome by the 0.2 pF or so lead capacitance. Note that the 4275A will display the dominant reactive component, so there could be 50 nanohenries or so of inductance but the lead/stray capacitance is greater. Theta (phase angle of the dominant reactive component) was about zero until 1 MHz or so then climbed to about 3 degrees at 10 MHz. Again, that's due to the capacitance of the component.
There was one precision 1K, 1W, 0.5% resistor that acted kind of screwy. It was the only one that had a dominant inductance, but even that was about 300 nH. The leads were fairly corroded on this one and its theta climbed much more rapidly as the test frequency increased. It was about 10 degrees at 10 MHz. This one might have been wirewound, it had a ceramic body
I think it's safe to say that the spiral trimmed resistors have no impact at audio frequencies. Once you get to RF all bets are off, but even so, lead inductance and stray capacitance seems to dominate.
Perhaps another audio myth busted...?
Maybe. I've always figured that if anything a tiny series inductance would help to get rid of RF getting into a grid since it would form a low pass. Never figured it would be enough to really matter even at RF but never had the data to prove it.
I'll just use it as an excuse to continue not buying carbon comp resistors.
I'll just use it as an excuse to continue not buying carbon comp resistors.