5E7 low volume... numbers posted...

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crashtm1
Senior tube assistant
Posts: 114
(2/25/04 8:57 pm)
 5E7 low volume... numbers posted...
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 I have had a volume problem for a while on this one...
I have re-traced all my wires and re-soldered also...
My bias reading on my Bias King reads 8ma,,,,ouch!!!
I assume this is the reason for the low output??

Here are my pin readings,,, any suggestions on where to start looking..???

1> GRnd.
2> Grnd
3> 494
4> 495
5> -44
6> -44
7> 0
8> Grnd...


Hope this helps.....
Thanks people.........:)
 
ganzonimx
Hey get your own solder
Posts: 407
(2/26/04 12:39 pm)
 Re: 5E7 low volume... numbers posted...
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 I suppose this reading is on the 6L6's - and the look strange indeed ...

Are you sure the Bias King reads correct? Are both tubes 8 ma? you might check with a 1 ohm res from pin 8 to grnd to make sure that the bias probe is working all right...

Cris.

 
Lucid Alice
Senior tube assistant
Posts: 167
(2/26/04 7:05 pm)
 Re: 5E7 low volume... numbers posted...
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 Pins 1 and 8 should be to ground. Pins 2 and 7 should be the heaters and should read 6.3v AC. If you're not getting full heater current the tube won't work right. Re-measure pins 2 and 7 on an AC setting and post your findings.
 
crashtm1
Senior tube assistant
Posts: 117
(2/26/04 7:40 pm)
 5e7 low volume
--------------------------------------------------------------------------------
 Ok.. Bias probe is fine..
I was a bit confused about the heater wires..
OK.. I have clipped 2 from ground, and hooked the heaters up to 2-7... voltage is now 3.5 at each...

On this note,, do I then continue the heater wires over to pins 4-9 like found on the 5E8??

Now when I switch on the standby, I can watch the bias climb from 0- 50 ma,,, then I start getting a loud continual "Woof" sound from the speaker... which I quickly power down/off after that..
 
6G6
Junior tube assistant
Posts: 95
(2/26/04 8:08 pm)
 Re: 5e7 low volume
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 If you have a bias adjust, I'd back off a bit. 50ma is too much at 495V. Maybe 30-35 would be better.
The heater wires need to go on to the preamp tubes.
Try to twist the wires together fairly tight and to get the same wire to each side of the 12whatevers. That is one wire to all 4-5 pin conections and the other to the other heater conection, I beleive that's pin 9.
 
ganzonimx
Hey get your own solder
Posts: 410
(2/26/04 9:16 pm)
 Re: 5e7 low volume
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 The original schematic/layout shows that the heater circuit uses the chassis as conductor for the heater circuit. I think the amp should have worked ok this way, unless there is a other error.

Double-check everything well.

By the way, is that a original ore a rebuilt?

Cris
 
crashtm1
Senior tube assistant
Posts: 118
(2/26/04 9:30 pm)
 5e7 low volume
--------------------------------------------------------------------------------
 This is from scratch.. Weber chassis..
Ok.. I will disconnect 9 from grnd and continue my heater wires over to 4/5-9 on the pres...
The bias isnt idleing at 50,,, that's just where I shut it down at,,, it was still shooting upward...
This is my 5th build from scratch,, but I'm always learning..:)
By the way,,, do my other numbers look good,, besides the heaters being wrong on my original post..???
One thing I might mention ,, while comparing voltage readings to the original schematics,,, I did find that on the big Cap (16/450),,, filter I assume,, that connects to the 56K Resistor ,then on to the 12ax7,,, Fender has approx. +332V,, mine was 432V... the other 2 caps were around 490V,, fender being @ 410V and 415V....

 
Lucid Alice
Senior tube assistant
Posts: 168
(2/27/04 10:27 am)
 Re: 5e7 low volume
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 Sorry, Sorry, Sorry. I was unaware that the 5E7 used the chassis in the heater circuit. I was just looking at the pin voltages and it looked to me like the tube was not conducting... Then I see the heater voltages and know something's not right.

Maybe the problem was that the heater center tap was grounded. Wouldn't you would have to tape off the center tap off for that method of heater wiring? If you didn't you would be shorting out half of the heater current and only get around 3 volts to the heaters.

The standard heater wiring you are going to should work fine anyway. It appears that the change has got the tube conducting.

Complete all the heater wiring before you measure voltages. If the tube isn't working it won't drop any voltage. That's probably why you are reading higher than normal voltages right now.
 
crashtm1
Senior tube assistant
Posts: 119
(2/28/04 9:07 am)
 5e7 low volume
--------------------------------------------------------------------------------
 I did some more voltage readings with the power tubes out. Im worried that I may do speaker damage with them in..
pins 3,4,5,6, all are reading about the same as before..
3,4 = 505V,,, and 5,6= -43v
I am still seeing about 100 more volts at various points in the circuit,,,
I checed out the bias circuit,,, would it be a good assumption that I have a bad resistor in this area, allowing too much neg. voltage thru??
I will sit down and trace all my circuit wires again tonight..
 
jbrew73
Junior tube assistant
Posts: 101
(2/28/04 10:23 am)
 Re: 5e7 low volume
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 after reading all the post i'm not clear on the heater wiring that you are using.
the original wiring with one side grounded will work ok or the more common method of wiring 2-7 on the power tubes and 4.5-9 on the pre's would probably be better but make sure to stick with one or the other throughout the entire amp.
once this is done i would measure all the heater pin voltages and make sure this is not yor problem. as someone else said above if the heaters are not working properly the tubes can't operate properly and this could be the reason for the high voltages you are experiencing. i would then repost all your voltages.
 
ganzonimx
Hey get your own solder
Posts: 411
(2/28/04 10:30 am)
 Re: 5e7 low volume
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 What transformer and what rectifier do you use? The high voltages are probably due to a transformer with a higher rating then the original.

how is the voltage now on the heaters trough the circuit?

Cris

 
Lucid Alice
Senior tube assistant
Posts: 169
(2/28/04 12:10 pm)
 Re: 5e7 low volume
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 With the tubes out there is no circuit. That is why the pins are reading high. A resistor off B+ that connects to nothing will read the same voltage on both ends. It is the current flowing through the circuit from ground that causes the voltage drop.

If your heater wiring is completed and your B+ is reading OK considering there isn't any current draw to bring it down (it will read high with no tubes in), then you need to plug in the tubes before you measure any voltages.
 
crashtm1
Senior tube assistant
Posts: 120
(2/28/04 12:35 pm)
 5e7 low volume
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 It will take time to get all the readings,,, If my bias sky rockets before i get them all,, can I cause damage to anything?
I have connected the heaters as follows..
From the pilot... to 2/7 on power tubes.. then on to 4,5-9 on the preamp tubes...with the grounds disconected..


 
crashtm1
Senior tube assistant
Posts: 121
(2/28/04 3:29 pm)
 5e7 low volume
--------------------------------------------------------------------------------
 As for my transformers..
I usually get them from David Allen , or Mojo..
But this set I must have gotten somewhere else. If anyone can help identify...
PT. = T542819
OT.= 318 0168
I did a bit of searching myself, but found nothing with similar numbers...


 
 
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