Firts start up Dumble

[Oddvar R]

Now I am finishing the Dumble build, and a bit above my skill to be honest. I am though wondering how the best initial testing / startup would be?

[martin manning]

I recall writing up a start-up guide for someone a while ago, but it may be hard to find. There are probably some web resources available, but the procedure depends somewhat on the circuit. I can find something later and post it. Probably this is a good topic for a sticky post.

[Roe]

use extra small fuses at start up.

[Guy77]

I like to run the amp through a variac when I first power up a new build. This way I dial up my voltages gradually until I get to 120v or 220 -240v for an overseas build. Variacs are such a handy tool !

Its amazing how different wall voltages can be from house to house, with the variac I know for sure the amp is at 120v and then I can check all the voltages in the amp while its running at 120v.
My dads place is running at 123v and my place is running at 117v.
Of course make sure your variac is properly fused and can handle the current for the amp your building.


Cheers

Guy

[10thTx]

Best advice I've read on start up of an amp is in this Hoffman thread with the advice from Sluckey (see Reply #3).

http://el34world.com/Forum/index.php?topic=2376.0

With respect, 10thtx

[sirbergs]

Best advice I've read on start up of an amp is in this Hoffman thread with the advice from Sluckey (see Reply #3).

http://el34world.com/Forum/index.php?topic=2376.0

With respect, 10thtx

Where do you find 75 watt incandescent bulbs these days?


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[martin manning]

They are still available, often as a specialty item such as an oven bulb. I like 60W with a clear glass envelope.

[pompeiisneaks]

Home Depot carries them:

https://www.homedepot.com/p/Philips-75- ... /202766537

~Phil

[sirbergs]

Nice


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[talbany]

Right before start-up I go through and check all my grounds 1 more time on each cap in the Power supply. Then meter out the + side of each cap make sure there are no dead shorts to gound.Then do the same for the bias supply and the rectifier diodes for the B+ make sure I don't have a shorted diode. From there if you like you can move to the preamp and check those grounds as well.
You are then ready to bring it up slow with a variac and a bulb limiter. I generally attach my meter right off the plate supply cap and monitor that on up. After I reach about 100 Vdc or so there I will go ahead and meter out each node again.If everything looks even. I'll go ahead and bring everything up again monitoring the plate cap supply. Once everything is full up and you have a dim bulb and everything looks OK. Adjust the bias supply to max - voltage (I generally like to see around -65/-70 V)
from there you can load in the preamp tubes make sure they light up and check all the voltages again. Now you're ready for the output tubes and the smoke test. Make sure you have a load on the amp. Pop in the tubes bring down the negative voltage until the tubes ae properly biased. If the amp makes a great big squeal noise you need to reverse the output transformers primary wires. Make one more sweep of all the voltages if everything is in spec or close. Plug in a guitar bring the vol up slow pray the thing works.



Tony

[norburybrook]

Then meter out the + side of each cap make sure there are no dead shorts to gound.Then do the same for the bias supply and the rectifier diodes for the B+ make sure I don't have a shorted diode.


Tony

Thanks for that Tony, I have had a bad diode once and it took me ages to find out what it was that test would probably have shown it.




M

[donvan]

Adjust the bias supply to max - voltage (I generally like to see around -65/-70 V) ...
Pop in the (output) tubes bring down the negative voltage until the tubes ae properly biased.
Tony

Thanks Tony. I'm saving your tips in my notes.

When I brought up my first amp I didn't check/set the bias BEFORE putting in the power tubes. I had an error in my bias circuit and the bias was zero volts. Those tubes were NOT happy.

[pompeiisneaks]

Very cool, yeah I think that would also be a great sticky if you make it an original post Tony. Then we could have others add any other tips to validate etc. One other tip I like from the el34world forums is to print out your layout and use a sharpie or something similar to double check every component and connection by highlighting them as present and correct before first power up.

~Phil

[talbany]

Very cool, yeah I think that would also be a great sticky if you make it an original post Tony. Then we could have others add any other tips to validate etc. One other tip I like from the el34world forums is to print out your layout and use a sharpie or something similar to double check every component and connection by highlighting them as present and correct before first power up.

~Phil

Cool! Phil will do.
Everyone has there own method of startup. I call mine the catastrophic checklist. It's really there to prevent sparks, tripped breakers red plating power tubes exploding caps and hot chassis.It also might save you a few fuses.

When I brought up my first amp I didn't check/set the bias BEFORE putting in the power tubes. I had an error in my bias circuit and the bias was zero volts. Those tubes were NOT happy.

You should always know your - voltage range on the bias supply before you even think about loading in your power tubes!!

Tony

[daniboy79]

I used both a Variac and a custom light bulb limiter I built.