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Of course, it makes a lot more sense. I don't know why I've connected Earth that way, but at least is is going to be an easy fix. As I've mentioned, I still have a lot to learn :dude:
Thanks to you and @2L man for pointing me in the right direction!
Cheers!
Thanks a lot guys!
I'm rather OCD, so I'm trying to do a neat build, but I'm still a rookie (this is my second amp), so I make a lot of mistakes :D
If I got @2L man's comment correctly, he suggests separating Safety Earth from grounding.
I indeed disconnected the last tag of the stripboard to...
After two much needed weeks of holidays, the amp build continues:
First I changed the routing of the output transformer primary to tubes’ plates connections as well as some mistakes I’ve made wiring the tube sockets. Thanks @Marcomel79 for spotting them!
Since I’ve finally received the...
Today I did some more work on the tube sockets,
adding the screen resistors, wiring the OT primary, and so on:
Wiring is still a bit of a rat’s nest. Still waiting for the lacing tape to get things tidied up. I’ve also added some taps to measure the bias of each tube.
I know it’s not the most...
Yesterday, I wired the two bridge rectifiers for the B+ and Bias supply.
I must admit it kicked my butt a bit more than expected. It's a lot of wiring to tuck in a relatively small area. Also, working with eyelets is far less enjoyable compared to turrets. When you have a single eyelet hosting...
Very nice work as usual Marco! Especially considering the challenges with the narrow chassis and the mods you have been able to squeeze in. Congrats!
The fixed/cathode bias switch is very interesting.
I might try it in the future, as I really would like to play with KT88s sooner or later.
I’m...
Today I finished the heaters circuit, wiring all the tubes sockets:
Meanwhile I’ve also started working on the stand by switch, where the B+ from the rectifier is going to be wired.
I’ve added a capacitor and resistor in parallel which should remove any pop:
The capacitor is 0.047 uF 630v...
Hi,
6V is the reading after the dropping diodes.
The highest voltage I’ve read on the heaters at the power supply is 7.06V. The lowest was 6.67V. That’s about a 5% difference which is the coherent with the fluctuation I get sometimes here on the mains voltage
I then proceeded to test the effect of my little contraption.
First of all, the pilot light turned on when I flicked the switch:
Then I measured the heaters voltage at the power supply:
and at the pilot light:
You might argue that 6.67 volts was still okay, but the mains voltage was...
The first task I wanted to tackle with the power supply section of the amp was the 6V heathers.
To start, the amp didn't have a physical center tap for the 6v secondary, and also, being built 60 years ago with contemporary AC mains, it was reading relatively high voltages.
I therefore decided...
This thread isn’t dead!
It has been months since my last update, but unfortunately my life in the last 12 months has become increasingly challenging. It’s not all negatives though, some challenges are definitely positive, but they mean way less time to dedicate to tube amps!
Anyway, I finally...
After testing the transformers, it’s time to start the build.
Since I’m using reclaimed transformers, any standard premade chassis is not going to work for me.
I have two options:
- Modify the original chassis
- Build a new one from scratch
Initially, I tried to reuse the original chassis, but...
That's actually what I used to start from and to do my measurements.
I needed to test that the output transformer was actually working and to measure its primary impedance, as I must use it with different tubes: 5881 vs EL34.
The output transformer is a very strange animal.
It has three separate secondary windings with intermediate terminals that connected in series or parallel can match speaker impedances ranging from 1.25 to 500 OHMS.
I managed to find an old datasheet that lists 4000 OHMS of primary impedance...