audio-talk

I believe I have this right but just want to "check my working".

For my 300B project, the circuit I'm basing it on has the power supply wired thus:



The power supply on the right uses the 6CJ3 which does NOT have the heater connection tied to the cathode. Therefore the centre tap of the heater supply has been tied to ground. The power supply on the left has an unspecified rectifier valve and also has the centre tap of its heater supply tied to ground (highlighted).

My plan is to use the GZ34 in both power supplies which, although indirectly heated, has the cathode tied to the heater. I believe that because of this, the 5v supply should not be grounded, with the idea being that it follows the changes in voltage at the cathode. Am I right?

Don’t whatever you do, ground the centre tap of the rectifier winding. You’ll burn out the mains transformer.

Cressy Snr wrote: ↑Sun Aug 16, 2020 2:53 pm Don’t whatever you do, ground the centre tap of the rectifier winding. You’ll burn out the mains transformer.

You could take the HT from the 5V centre tap.

pre65 wrote: ↑Sun Aug 16, 2020 3:01 pm

Cressy Snr wrote: ↑Sun Aug 16, 2020 2:53 pm Don’t whatever you do, ground the centre tap of the rectifier winding. You’ll burn out the mains transformer.

You could take the HT from the 5V centre tap.

Exactly

So I'm right in other words

I was looking at the Olson drawing and suddenly thought - hang on, with a GZ34 that's a short circuit waiting to happen.

To be faiir, it had probably been quickly edited to use a recifier instead of the diodes and doesn't specify any link between the cathode and heater.

The gz34 and 6cj3 are indirectly heated so take the HT off the cathode.

The 6cj3 is a damper and has very high heater cathode rating. Not so gz34.

Ref the gz34 heater to the cathode.

The symmetric reichert has some left overs from the karna and do can be a bit confusing.

Yep, the damper diodes can stand that voltage between the heater and cathode, the indirectly heated normal rectifiers can't, and the directly heated has no cathode. Also make sure when you get the transformer wound that the heater winding is spec'd to run at the voltage you are intending to use it at. You can use a simple toroid with the damper diode and ground the heater supply to protect the transformer. A normal rectifier would need a heater winding that's safe to run at 600v or so above the core.

Although the sym reichert is a thought experiment, I'm guessing Lynn will have drawn it to use a dual damper for the front end and so could ref the heater to ground (probably). Maybe 6by5. 6cj3 would have been completely ott for 6sn7 front end. In the Karna he ran all 4 6cj3 from the same winding and so ref'd the lot to 0v.

Nick wrote: ↑Sun Aug 16, 2020 5:36 pm Yep, the damper diodes can stand that voltage between the heater and cathode, the indirectly heated normal rectifiers can't, and the directly heated has no cathode. Also make sure when you get the transformer wound that the heater winding is spec'd to run at the voltage you are intending to use it at. You can use a simple toroid with the damper diode and ground the heater supply to protect the transformer. A normal rectifier would need a heater winding that's safe to run at 600v or so above the core.

I'm planning on using two off-the-shelf Hammond models, the 375X and 378X rather than custom wind (in an effort to stop costs completely spiralling out of control ). Both have 5v and 6.3v secondaries and I'm anticipating that the 5v winding was intended for use with rectifiers. The datasheet only mentions primary to secondary maximum potential difference, given as 2500V.

Thermionic Idler wrote: ↑Sun Aug 16, 2020 7:16 pm

Nick wrote: ↑Sun Aug 16, 2020 5:36 pm Yep, the damper diodes can stand that voltage between the heater and cathode, the indirectly heated normal rectifiers can't, and the directly heated has no cathode. Also make sure when you get the transformer wound that the heater winding is spec'd to run at the voltage you are intending to use it at. You can use a simple toroid with the damper diode and ground the heater supply to protect the transformer. A normal rectifier would need a heater winding that's safe to run at 600v or so above the core.

I'm planning on using two off-the-shelf Hammond models, the 375X and 378X rather than custom wind (in an effort to stop costs completely spiralling out of control ). Both have 5v and 6.3v secondaries and I'm anticipating that the 5v winding was intended for use with rectifiers. The datasheet only mentions primary to secondary maximum potential difference, given as 2500V.

That should be fine. Will be on a bobbin unlike a typical toroid.