Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: GilSt on January 17, 2012, 08:04:18 AM

Title: Questionable voltage readings, should I proceed?
Post by: GilSt on January 17, 2012, 08:04:18 AM

Hello.

First, let me express my deep appreciation of your work. Being my first DIY project, stock Crack assembly was easy and it sounded great!

Yesterday I finished the speedball upgrade, plugged in and the left PC board didn't lit its LEDs.

After rechecking I found my mistake - attached black wire to wrong terminal: instead of G - to a near-by R4 one. (bottom image on Page 22 of the manual)
After the correction, everything lit up properly, and I started with the voltage check.
Those are the voltage readings:

Terminal   Expected   Actual
1             75             84      
2             170             155
3             0                0
4             170             155
5            75             108
6             0                0
7             100             101.7
8             0                0
9             100             117
10             0                0
11             0                0
12             0                0
13             170             154.3
14             0                0
15             185             173
            
20             0                0
21             206             192
            
A1             75             107
A2             0                0
A3             1.56             1.54
A4             0                0
A5             0                0
A6             75             83.4
A7             0                0
A8             1.56             1.54
A9             0                0
            
B1             75             83.3
B2             170             153.3
B3             100             101
B4             75             108
B5             170             153.5
B6             100             117
B7             0                 0
B8             0                 0

Some of the readings exceed even 15% margin.

Should I proceed to final check?

Thanks!   

Note: We ordered a batch of 3 kits. Another member reports very similar results (haven't been able to contact thrid member yet). He also reports a slight static noise in left channel.

Title: Re: Questionable voltage readings, should I proceed?
Post by: Bolivar on January 17, 2012, 08:48:22 AM

I had very similar voltage readings at first with my crack + speedball. Replacing the 12AU7 driver tube solved the issue.

Title: Re: Questionable voltage readings, should I proceed?
Post by: Paul Joppa on January 17, 2012, 09:52:05 AM

Yes, it looks like one section of the 12AU7 is low on transconductance. It may come around in a while - like, 50 to 100 hours of operation. New tubes sometimes do not have the cathode emission fully developed. Nothing is so far out of line that it will cause harm.

Title: Re: Questionable voltage readings, should I proceed?
Post by: GilSt on January 17, 2012, 10:36:22 AM

Thanks for the replies.
As advised I replaced stock tube to a JJ 12AU7  (also new) and the readings are now fine (except 170V are all 155V).

The sound is now amazingly crispy. Sennheiser veil is long gone.