Wednesday, June 23, 2010

Blog switching over to Posterous

I'm switching my blog over to Posterous.

The new blog can be found at Just did the manual porting of 165 posts that I have done since Jan 2007. The old one will still remain though.

Posterous offers means to blog via email and also an iPhone app. Just perfect for me to do small postings. ;)

Let's hope this will improve my attempt to put new stuff onto the blog. Hahaha...

Wednesday, June 16, 2010

26 DC 45 amplifier - updated schematic

There goes thoughts of re-using the power transformers. B+ after regulation has to be around 455v. I probably need around 500v prior to regulation. This also means the capacitors would need to be put it series or to use the huge oil types. Unfortunately, I only have three 660vac oil run capacitors. The rest are 370vac types.

Now, I'm starting to wonder if the C4S can drop that much voltage. Is it able to handle the wattage?

VoltSecond has some useful information about implement the C4S at his site. Just reading off the chart, it is best to keep the C4S under 300v across the MJE350. One easy way is to drop the voltage with a resistor prior to the C4S. At 5.5mA, I would need a resistor of 30k ohms to drop the voltage to 290v at the top of the C4S. This will result in a R2 at the C4S of 145k ohm.

Tuesday, June 15, 2010

26 DC 45 amplifier

So, here's the scribble on paper. Operating points are pretty standard stuff for 26 and 45. The brief is simple... DC coupled amp, with driver C4S loaded and with LED biasing. Filaments will be DC current regulated. B+ will be regulated by a HV Maida circuit. Tamura F475 is intended to be the output iron, but I may A/B the FT10S that I got from Andix.

Chassis will be a departure from the tower types that I have been building. I'm veering more to the Fi designed ones. Wanted my wife to lug any fi stuff back when she was in New York some time back, but boy, there's a long back log being fulfilled by Don Garber.

Anyways, since the 6T10 project was not successful, I should look for another project that can hopefully reuse the power transformer. The 45 fits the bill as I've already got suitable output transformers and even a pair of RCA 45 tubes. I've also got a stash of 26 driver tubes. This will be my first all DHT amp. Wonder what challenges I will face... Should prototype this on a board first... ;)

Work on this hopefully will start at the end of this month.

ps. an eagle-eyed reader highlighted that my schematic has some mistakes around the cathode resistor for the 45 tube. i've forgotten to stack the driver voltage for the DC arrangement. will update the schematic tonight. thanks nick!

Monday, June 14, 2010

Universal Studios Singapore

Went there last Saturday. Was a sunny afternoon and it was a weekend, plus the school holidays. Queues were generally long. The Rapids Adventure has a 80 mins queue...

Lucas quite enjoyed the Enchanted Airways ride at Far Far Away. The show at Far Far Away was ok, but I thought they over did the water spraying portions... Disney had the same type of shows too.

I thought the Revenge of the Mummy ride at Ancient Egypt was good. The queue was only 10 minutes. The walk in was long and winding though. Treasure Hunters was a let down. 40 mins queue and was a total waste of time.

I went with Lyra to Madagascar's Party-Go-Round (basically a merry go round). She dare not take the animals, so we ended up on the crate instead.

Waterworld was so-so. I did not quite enjoy it.

All in all, the park was small. But San thought it was better than Hong Kong's Disney.

Some pics here.