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TubeHound 4th January 2003 05:24 AM

JE Labs 300b round 5. MUSIC!! MUSIC!!
2 Attachment(s)
Hi Everyone,

Thanks Frank, John and everyone else that helped. The amp is working quite well. It plays MUSIC!! and sounding better with every hour. Meter still dose not work right, I'll fiqure that out. Heater volts for 300b is high and will work on that. It sounds wonderfull. Thanks to for a great forum and to all that helped a new guy get started in this hobby. Here is a pic of the amp and myself, the amp is much better looking. Oh, my wife is thrilled.

BrianGT 4th January 2003 05:30 AM

Congratulations, it came out really nice!


analog_sa 4th January 2003 06:49 AM


Oh, my wife is thrilled.

Great tip! I'll see if i can thrill my wife too :)

dhaen 4th January 2003 08:43 AM

Well done.:cool: :cool: :cool: :cool:
It looks good complete too!

I'd posted to your original thread before I saw this one.;)

Don't leave the heater volts issue too long, it'll shorten the tube's life. Also they might not work as well when you eventually correct the voltage.
Funny, I only thought about that yesterday. It's probably because you are using Schottkys.

Burnedfingers 4th January 2003 12:48 PM

Great job on the metal working and for that matter the whole amp.

You can be very proud.


fdegrove 5th January 2003 12:47 AM


Does this amp look good or what!!!

Congratulations Paul,a formidable job you did.


Don't leave the heater volts issue too long, it'll shorten the tube's life. Also they might not work as well when you eventually correct the voltage.
Especially if it's over 10% of the 5V rating.

I'll do a :headbash: session for having overlooked the high efficiency of the Shottky diodes.


Meter still dose not work right, I'll fiqure that out.
Is it just inaccurate?
If so,a trimpot is the easiest way IMO.
When connected in series with the meter adjust it till the readings from DVM and panelmeter correspond.
Measure the resistance of the trimpot at that posistion and replace with a close enough standard value.

Happy listening,;)

TubeHound 6th January 2003 03:16 AM

Thank you
Thanks guys for the compliments.

Both are now up and running. The heater voltage for the 300b filaments are way to high. On one I used a 100ohm resistor and the other a 1.1k resistor. The 1.1k is actually higher at 9.5 volts and the 100ohm is at 7.2 volts. How do I correct this? The resistor is in series with the posistive lead coming off the diodes into the first of two 10v 10k uF capacitors. The caps are coupled on the posistive lead by a choke. Anyway, they sound great and once again I really appreciate all the help and friends I've made here. Should I put a resistor in series with the negative path?

dhaen 6th January 2003 07:57 AM

Switch off straight away!
As Frank said 10% high is the safe maximum.
Where are these resisitors you're talking about?
They can't be in series with the heaters - not enough current would flow. We should be talking an ohm or 2.

The resistor to alter will be either in series with the rectifier bridge, or, between the 2 positive terminals of the heater supply smoothing caps.

There is some advantage to having a resistor in both top and bottom of the heater supply smoothing, but you must make sure that the grounding is done on the tube side of the bottom resistor.

fdegrove 6th January 2003 08:18 AM

RE:Switch off straight away!

Where does this 9.5 V come from?

The 7.2 volts correpond with the rectified 5 VAC and as D'haen suggests should be reduced to 5VDC by inserting the resistors.

Paul,if these voltages are correct you're permenantly damaging the 300Bs.
As it is now even the 10V caps can blow up as well.


If you could make a drawing of current wiring of that part it would surely help.


TubeHound 6th January 2003 01:01 PM


I think I know what is wrong. When I built the circuit, the trace for the resistor goes straight through, no break. Hence, the electricicty goes around the resistor or straight through, no need to jump up into the resistor, does'nt have too. So, any suggestions on resistor values? I believe the 9.2v is coming from the PWT it was just wound wrong, should be easy to tame, same for the 7.2v. Will let you know and thanks for your help again. Oh, on the post for wiring the amp I posted a diagram of the circuit, if you refer to this, it will show where I made my mistake.

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