Crack;Bottlehead OTL - Page 111

Sounds like your tubes have some heater-cathode leakage. The solution is to use a different tube.

Quote:

Originally Posted by Doc B. 

Sounds like your tubes have some heater-cathode leakage. The solution is to use a different tube.

OK, will do!   This  humming noise comes and goes if you tap on the tube with a pencil and then comes back after a bit.

Is there a technical reason for what's happening like part of the guts that aren't supposed to be touching actually are, or something?  The guy I bought the tube from claimed it tested 95/95 and had 'no microphonics.'    Meanwhile if you tap it lightly with a pencil it sounds like a mule kicking a spring reverb in a guitar amp.

Well, maybe he meant that it had no microphonics when it was not plugged into an amp. 

I gave him the benefit of the doubt that the postman was playing football with the package on the way to my house.

The hum isn't all that loud (you quit hearing it as soon as you start playing music at low volume.)    How risky is it to use leaking tubes though in terms of them going 'full short' ??

As long as it isn't crackling or popping it will probably be OK. And sometimes the hum can reduce with some burn time. Sometimes not.

This is a circa 1943 RCA 6AS7G.  I noticed people online doing things like baking them in the oven to 'dry out' the bakelite base in case of shorting that way.   I presume the heat generated while being used would cause that moisture to flee the base though.    I'm going to test the 'bulb' from the base to make sure it's not loose tonight.  I'd love for it to quiet down because I really like the way it sounds.     I need to befriend someone locally with a tube tester and the knowledge required to use it.  

How do the pins look on that tube silverhead?  Back in mid-2011, I had an RCA12bh7 blackplate with an unfortunate hum issue, and Doc suggested buffing the pins with fine steel wool as a possible fix.  I used fine grain sand paper, in the absence of steel wool, and then inserted and removed the tube a dozen or so times.  The hum was completely eliminated.

I don't know if this has the same probability of success on a power tube, but I figured it would be worth tossing out there.

I get after everything that comes to the house with Caig DeOxit D5 and Q-tips.   I can try to burnish the tips, but they're already pretty clean and newish looking   I have 00 steel wool to try though.   My guess is that it took a hard knock on the USPS truck.  I have more coming in the mail.

I've been trying to score oddball 12AU7 equivalents to see what sort of differences I hear as well.  It's been fun.  

does anyone know what this amp is worth fully assembled & built without the upgrade kit?

Quote:

Originally Posted by igotyofire 

does anyone know what this amp is worth fully assembled & built without the upgrade kit?

Hard to say. I've been looking around for awhile and it seems they basically go for the price of the kit, if they are built well. Everything I've read on the bottlehead forums is pretty wary of buying prebuilt kits because if any issues show up down the road they are hard to pinpoint. If the kit isn't built well it could easily be a mess. 

edit: Should also add you shouldn't sell the kit for more than it costs directly from bottlehead on the head-fi forums unless you are a member of the trade. 

Is it sold as assembled or only diy kit ?

Quote:

Originally Posted by richbass 

Is it sold as assembled or only diy kit ?

it is a DIY kit, but bottlehead will assemble it for a fee im pretty sure. I was part of the first groupbuy i believe for the Crack amp . I don't really use the amp anymore but still deciding on whether I want to keep it or not, I have an emotional attachment too actually since I built it.  I haven't been on head-fi for awhile, pursuing other hobbies. The only thing I cant seem to live without is IEMs though. 

We no longer build amps for customers. My techs are hired for R&D work and they don't have the time to fit kit assembly into their schedule any more. But anybody can build one of these kits. There are literally thousands of Bottlehead kits out there that have been built by beginners.