Rail voltage imbalance.

pjblakey · 26th June 2011, 09:54 PM

I have put together an F5 type amp using a tubeshunter kit.
I checked the power supply with no amps connected and the rectifier and output voltages remained stable at +/_ 26VDC for 30 minutes. I am using an Avel 250VA 18+18 transformer.
When I connected the left channel, the rail voltages immediately began to drift upwards on the negative side with the bias pots at 0 ohms(or close). The voltage peaks at close to -46VDC and +6VDC.
Right channel ditto.
I have checked the mica insulators, made sure of amp ground to PSU, looked for broken tracks and dry solder joints.
Before I realized this was happening, I did manage to adjust the bias current to !.3amps, but the amp shut down. No blown fuses. either 1 amp or 2.5amp fast blow.
Has anyone had a similar experience or any bright ideas?

Cheers

Peter

semi932 · 26th June 2011, 10:23 PM

Definitely something in the boards as you say the voltage is ok coming out of rectifier and caps.

Check and make sure fet's are installed correctly for starters.

Also the ztx transistors are oriented correctly.

Bill Fuss · 27th June 2011, 12:17 PM

I hope you didn't expect a lot of help, seeing that you are using pirated Chinese boards.

Andy5112405 · 27th June 2011, 12:39 PM

Try loading the PSU with resistors just to check that everything is OK.

h_a · 27th June 2011, 05:43 PM

Ground of +-rail and --rail connected to eachother and connected to safety ground? (Sounds like a floating ground to me).

Hannes

pjblakey · 27th June 2011, 09:03 PM

Thank you for the responses.
After further inspection of the solder joints and component orientation and functioning, I'm pretty sure that it is a grounding issue. Have to check when I return from vacation.

Peter

26th June 2011, 09:54 PM	#1
pjblakey diyAudio Member Join Date: Mar 2009 Location: Smoky Mountains, NC	Rail voltage imbalance. I have put together an F5 type amp using a tubeshunter kit. I checked the power supply with no amps connected and the rectifier and output voltages remained stable at +/_ 26VDC for 30 minutes. I am using an Avel 250VA 18+18 transformer. When I connected the left channel, the rail voltages immediately began to drift upwards on the negative side with the bias pots at 0 ohms(or close). The voltage peaks at close to -46VDC and +6VDC. Right channel ditto. I have checked the mica insulators, made sure of amp ground to PSU, looked for broken tracks and dry solder joints. Before I realized this was happening, I did manage to adjust the bias current to !.3amps, but the amp shut down. No blown fuses. either 1 amp or 2.5amp fast blow. Has anyone had a similar experience or any bright ideas? Cheers Peter

27th June 2011, 05:43 PM	#5
h_a diyAudio Member Join Date: Sep 2006 Location: Graz, Austria	Ground of +-rail and --rail connected to eachother and connected to safety ground? (Sounds like a floating ground to me). Hannes __________________ fresh matched IRFP240/IRFP9240 fets \|\| AlephJ/JX-kits F5 transistor kits \|\| Burning Amp BA-1/2/3 transistor kits

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26th June 2011, 10:23 PM	#2
semi932 diyAudio Member Join Date: Nov 2009	Definitely something in the boards as you say the voltage is ok coming out of rectifier and caps. Check and make sure fet's are installed correctly for starters. Also the ztx transistors are oriented correctly.

27th June 2011, 12:17 PM	#3
Bill Fuss RIP Join Date: Oct 2005 Location: Central Florida	I hope you didn't expect a lot of help, seeing that you are using pirated Chinese boards.

27th June 2011, 12:39 PM	#4
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	Try loading the PSU with resistors just to check that everything is OK.

27th June 2011, 09:03 PM	#6
pjblakey diyAudio Member Join Date: Mar 2009 Location: Smoky Mountains, NC	Thank you for the responses. After further inspection of the solder joints and component orientation and functioning, I'm pretty sure that it is a grounding issue. Have to check when I return from vacation. Peter

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