|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
72.235.7.37
I just finished wiring up my RH "universal" amp with 7591 tubes and it fails to make any sound thru the speakers. I ruled out all the variables, tubes, speakers, cd player, which only leaves the amp at issue. I checked all of my wiring against the schematic and found no errors. I checked, double checked, voltages on all the tube socket pins and all voltages are in the "ball park". This is a real head scratcher. One thing is the B+ is 300vdc for the output trans and 250vdc for the driver tube B+ which is maybe 10% less than recommended. Any tips and ideas for me to check out would be appreciated. Happy holidays, Dak
Edits: 12/09/14Follow Ups:
Then set your VOM to AC and look at R1 ref to ground. The numbers on the VOM numbers should be bouncing around. If not, well, the input tube is not ampilyfing.
Lounge Audio LCR MKIII
http://www.newrecordday.com/lounge-audio-mkiii-lcr-phono-preamplifier/
Edits: 12/11/14
Sounds like your voltages are nominal, if 'in the ballpark' is correct.
So you can go about this two ways. You can signal trace it, or signal inject it.
With injection you would pump the signal in through a coupling cap to the grid of the power tube. In this case have the driver tube out of the socket. If it works the problem is with the driver tube.
With tracing you observe the progress of the signal through the circuit. Lacking a scope, get a cheap amp (preferably tube, they are a lot harder to damage) and set up a probe consisting of an audio cable with a small coupling cap on the end of it, tied to the input of the cheap amp.
Look for the signal by putting the open lead of the cap on the cable (which we will call the 'probe') on the plate of the driver tube and see if you can hear anything. If not, go back to the grid of the driver tube. Maybe the signal just isn't getting to the grid....
In this manner you will find the problem very quickly. Be on the lookout for subtleties like in correct resistor values (maybe a red band where it should by orange or yellow), signal wired into the cathode rather than the grid, that sort of thing.
You can check out the schematic here;
http://rh-amps.blogspot.com/2013_01_01_archive.html
Thank you for your suggestions. regards, Dak
.
Have Fun and Enjoy the Music
"Still Working the Problem"
I am using 7591 tubes and 12ax7 driver tube. My B+ is 300vdc which gives 280 v on the anodes.
The 7591 power tube requires changing the voltage setting resistor of the LM317 to 18ohms for about 70ma dissipation.
Also the anode to anode feedback resistor is 200k ohm for the 12ax7 front end. Dak
LM317 is dead. Disconnect LM317 pin 1 from the cathode and place a 500 ohm 10 watt resistor across C1 and test for audio out.
I suppose that could be true but both channels? They were brand new when I installed them and all the others from this lot were good. The voltage reading at the cathode is almost 7vdc which again is in the "ballpark". I will probably give it a test anyway, since I have no idea why I have no sound. thank you for the suggestion, Dak
It is easy to wire a LM317 wrong.
I checked my other amp with the LM317 and it wired correctly. thanx
The chances are high that it has something to do with your assembly :)
In order to troubleshoot this over a forum, you need to assist the troubleshooters. Publish the schematic here for easy reference, and also photos of your build.
Also: the schematic will have voltages to be expected. Please publish your actual voltages.
Then this will go fairly quickly.
Is one terminal of the speaker grounded?
Lounge Audio LCR MKIII
http://www.newrecordday.com/lounge-audio-mkiii-lcr-phono-preamplifier/
Edits: 12/09/14
That's what I smell when I look at the schematic.
Lounge Audio LCR MKIII
http://www.newrecordday.com/lounge-audio-mkiii-lcr-phono-preamplifier/
Edits: 12/09/14
I am pretty sure I got that right. I measure the voltage at the cathode at about 10vdc. I think that is in the "ballpark".
Hey, you built a cool amp and you're not gonna show us pics??
Anyway, try this -With the amp running, put a low voltage 60hz signal into the input, like .5V or something... If you don't have a signal generator, then you could make an ersatz source by using voltage dividing resistors and the filament supply.
Now use your meter on the AC setting to see where the signal dies. Does it appear at the input to the inverter? The output of the inverter? The grids of the power tubes? etc....
Rule out large sections of the circuit all at once. Measure each point with and without test signal applied, to rule out bad readings.
Did you miss a ground?
My guess is that if you don't hear crackling from the speakers as you probe around, your output stage isn't working.
Edits: 12/09/14 12/09/14 12/09/14
I will try to post some pics. I do hear a very low level tick when I touch my meter probe to the G2 pin. which measure about 290vdc
Another set of speakers = still no noise? No muting section problems? Input switch issues? Phase inverter sections ok?
Output trannies wired correctly? Heater lines ok?
Hi FL, the RH universal is a SE amp with a pretty simple circuit. Mine is hardwired and I am so surprised that I don't get any sound from it. I have double , triple, quadruple checked all the connections and don't see any assembly, or wiring errors. Dak
Is one leg of the secondary off the OPT grounded? The input's voltage divide hooked up properly? All cathode-tied resistors ok?
Secondary is grounded to a separate ground along with the input jack grounds.
The driver tube B+ is obtained from the mains B+ and dropped via 105k resistor with 50uf of capacitance.
Cathode resistors, 1w mf were checked before installation and are grounded to a 12awg bus bar which is grounded to a power transformer mounting bolt.
It seems like I may have wired the driver tube socket incorrectly but I have checked the arrangement 3 times and do not see anything wrong. regards, Dak
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: