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Tubelab Discussion and support of Tubelab products, prototypes and experiments

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Old 15th October 2008, 12:46 PM   #11
cjkpkg is offline cjkpkg  United States
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Looks like I may need to beef up R17 and R27 to a higher resistance to maybe the 700-800 range.
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Old 15th October 2008, 12:52 PM   #12
Ty_Bower is offline Ty_Bower  United States
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I just tacked an extra 250 ohms in series with the existing 560 ohm resistor. Send me an email, and I'll mail you a pair.

Here's a photo of mine:
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Old 15th October 2008, 01:01 PM   #13
Tubelab_com is offline Tubelab_com  United States
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I plugged in the choke
If you are using a choke you should not be using R1, remove it. They are wired in parallel so you can use one or the other.

If R1 was glowing, and is now dead, there is a short somewhere. It may be intermittent, and may return to bother you again later. Please check over the wiring for anything that could be touching. If the board is mounted over a metal chassis make sure that the long pins from the electrolytic caps and tube sockets can not touch anything. If you have not mounted your transformers to a chassis yet, measure the case of each one to make sure that one of them is not hot with voltage. This is rare but it can be deadly.

As I stated in the manual every piece of metal in the amp must be grounded through the third pin on the power cord. This is usually automatic when everything is mounted to a metal chassis which is connected to the ground pin. You should have a fuse in the primary circuit. A cheap 2 amp fuse from Radio Shack will save the power transformer.

When I first started building these amps I was getting about 460 volts of B+ with SS rectification and 430 with a 5AR4. It seems that Hammond may be saving copper by leaving off some primary turns. My old 6K7VG makes 380 volts in my Simple SE with a 121 volt line, now we are getting 397 volts. I think that rasing the cathode resistors to 620 or 680 ohms with 6L6GC's is not a bad idea.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 15th October 2008, 01:27 PM   #14
cjkpkg is offline cjkpkg  United States
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Thanks George...R1 has been removed and I have implemented the fuse. I will definitely be triple checking all ground continuity as I complete the assembly on the new chassis.

My thought is that R1 blew along with the FREDs and the 5AR4 when the hot from the old PT shorted on the bell housing.

I plan to run tube rectification eventually so that may kick down the voltage just enough.

Thanks George and Ty for all your help.

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Putting the Simple SE back together - blown PT - Flashing RectifierHide this!Advertise here!
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