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Old 4th January 2004, 02:28 PM   #11
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?

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Old 4th January 2004, 02:45 PM   #12
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Iíve done the s‚me with 6.3V execpt there was no need to get another tranny..... .....desperation....except I used Schottky diodes (SB340 etc) with lower forward voltage losses than standard diodes in discrete bridge
The input stage in my amp uses 2x7199ís, initially the hum level was shocking. The heater current for the pair is about 0,8A, so I lifted the system 6.3V 20A off ground and used Schottky diodes to fullwave rect into a 10,000uF 10V elect. The DC volts available to the 7199ís is somewhat higher, and I used lo ohm resistors either side of DC to bring the down to 6.3V with another 3300uF slapped on. There was no need to use Lo-drop-out-reggies as the in /out differential was to low. After doing this, I biassed the whole heater chain to minus 10V. That cured every snippet of hum and now I can use different makes of tube. Bear in mind 7199ís vary alot but.... this recipe may not hold for other tube types. Botch it it up first.......
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Old 4th January 2004, 02:53 PM   #13
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Hi,

Quote:
Is Radiotron's 4th Edition worth the $40 - 50 it's currently selling for? I'm having a bit of trouble finding a copy in the UK. Postage from the US is substantial for a book that weighs this much.
It certainly is worth every cent of it if you're serious about valves.

On the net Tubecad is a good source for more modern applied circuits:

TUBECAD

Cheers,
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Old 4th January 2004, 05:24 PM   #14
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Hi there...Frank..interesting correlation regarding tube heater findings.....; have you got that version of Tubecad ? If so, how would you rate it......how detailed is the valve inventory ?

regs rich
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Old 4th January 2004, 05:26 PM   #15
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I think Frank's referring to tubecad's online journal, which is freely accessible by anybody and has a bunch of very useful and informative articles.

I found Morgan Jones' 'Valve Amplifiers' book to be very good as a first-time introduction to tube circuits.
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Old 4th January 2004, 05:34 PM   #16
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Quote:
Originally posted by fdegrove
Sorry if I sound rude but I start to get fed up with elemantaries...
This is a completely inappropriate comment for DIY. This is a forum for people to learn. Otherwise, it will just be a place where (rather hostile) elite come to flame each other.
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Old 4th January 2004, 07:11 PM   #17
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Sinc apol's for the confusion.......remember other foreigners also read these sites......patience....some of us can't be expected to get all intreprets perfect.......as those who have english as the cue language (mine is 2nd)....I see that reply as an insult.....

Each day I get loads of multi-lingual emails from other sites, some are trivial natured but I do promise sincere replies.

tschŁs

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Old 4th January 2004, 07:39 PM   #18
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Mods, delete previous remark please.
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Old 6th January 2004, 06:41 PM   #19
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Since I last posted I've ordered a copy of Valve Amplifiers. I have 6 pounds in book vouchers to spend, so it seemed like a good way to use them! I'm really looking forward to having something in paper to read for the next few weeks.

I also got some part thru for a new supply this morning. RS is quite possibly the most incredible retailer I've ever delt with. They're only really matched by The Hi-Fi Collective, in terms of response alone. I'll be on first names basis with the guy from Omega who delivers RS's parts soon enough.

The supply works perfectly now. So far I'm really happy.

One strange thing happened though.

[If you really have an empathy with tubes, leave the thread now]

I have a number of old El34's sitting around doing nothing. They're very old and have taken some serious wear in an A/B amplifier. In fact, they're so old and worn, they just blow the fuses when they're run. It's a Marshall amp, don't worry!

I decided to see how high the heater voltage could be taken before the heater's life time was exponentially shortened.

Well, the supply only manages 10Vdc, but the tube was glowing like a light bulb. It felt so nice to sit in an almost dark room light only by the heater of a tube. Which gives me an idea for a really cool lighting project... but anyway...

The tube began to tick as the voltage was lowered back towards 6.3v, perhaps around 5 - 10hz. I assumed it was simply moving as the temperature changed, but a minute or so later the ticking still hadn't stopped. So I increased the voltage again. From 6.3 - 8 volts the ticking began to decrease again.

The tube was not ticking before I raised the heater above it's normal operating voltage.

I now looked over at my scope. There was a lot of pulse like modulation on the voltage with a drop to a flat, but elevated, plane every 5 - 15 pulses. If I remember rightly, the scope was set to 20ms per division for it's time base and 5v per division for it's amplitude.

The ticking was loud enough that you could hear it in a quiet room from roughly 2 foot away. But anymore than that and it was almost impossible to hear.

I figured something must have been going wrong in the supply or the heater itself was going. I swapped the tube for an equally worn out EL34 and switched the supply back on. No ticking, and no nasty modulation.

The scope is a Fluke 123, which is probably the coolest thing in the entire house right now. When it's connected to an input, in automatic mode, it fine tunes itself to display whatever majority signal it detects. But with the new tube it simply sat still and didn't bother going any further.

Okay... I know the tube is almost certainly damaged; it couldn't have been used for anything other than an ornamnet anyway. I've smashed a few of them just to look inside. But what could have happened to the heater to produce these effects? I believe the tubes are gassed quite badly. Possibly something to do with the effect?

The ticking seemed to be quite close, in frequency, to the flat parts of the modulation.

I wish I had the SCC and Scope View option now. I could have sent you a piccy of it! The pulses d

I have some questions regarding the LM350T I am using for the voltage regulation. If anyone would be willing to help me with them I'd really appreciate it.

Now I'm stuck until the B9A sockets arrived really.

You've all been a great help so far!

My best wishes,
John
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Old 7th January 2004, 12:11 AM   #20
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Hi,

Yeah....
Whatever life was left in the EL34s is bound do be dead now...Sigh.

Quote:
I have some questions regarding the LM350T I am using for the voltage regulation. If anyone would be willing to help me with them I'd really appreciate it.
Why a 350 in the first place?

Nevermind, what do you want it to do?

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