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Author Topic: New 5X3 build no sound help  (Read 16106 times)
cmoore
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« Reply #15 on: February 21, 2011, 10:03:38 PM »

I definitely think you want to go the other direction. Try a 270, 280, or 300 ohm cat resistor.
That will get you current down a bit, without going to "thin" I think.
70% of a 30 watt tube is 21 watts. And, are you sure about your numbers.? 65mA per tube is almost double the "normal" current for a 6L6.
JMO of course....
Best
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davohilts
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« Reply #16 on: February 21, 2011, 10:24:19 PM »

Hi, and thanks for the help.
The 62milliamp was generated by the Weber calculator I was using.  I measured the milliamps on my power tubes and they are 52 which I thought was high but then not really understanding what I'm doing I was unsure which way I should go.  The spec on the build I'm doing calls for a 270 ohm 10 watt resister but I couldn't find one so I went with the 250 ohm.  I could probably use a couple of resisters in series to get into the range which would lower the current down into the mid range.
Thanks for the shove in the right direction.
Dave
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cmoore
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« Reply #17 on: February 22, 2011, 12:08:21 AM »

Would it be financially hard for you to order some high power resistors from Mouser.?
I do not mean to pry. You can email or PM me if you want to take this off-line.
I can mail you some 10 watt resistors if there is a need.
Keep in mind, the 270 on the schematic is somewhat of a "theoretical" value. In the end, you need to use what works to get the amp working properly.
To back track for a minute....are you sure about that 32.5 VDC across the cat resistor.?
Anyway, if I can help, let me know.
Wyatt is the one with a lot of knowledge about this stuff. He got you started, I should probably just let him get you through this.
Best
Hi, and thanks for the help.
The 62milliamp was generated by the Weber calculator I was using.  I measured the milliamps on my power tubes and they are 52 which I thought was high but then not really understanding what I'm doing I was unsure which way I should go.  The spec on the build I'm doing calls for a 270 ohm 10 watt resister but I couldn't find one so I went with the 250 ohm.  I could probably use a couple of resisters in series to get into the range which would lower the current down into the mid range.
Thanks for the shove in the right direction.
Dave
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davohilts
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« Reply #18 on: February 22, 2011, 11:03:48 AM »

the only thing that was stopping me from getting the proper value or range of values for the resistors is my own stupidity. I looked around several months ago and couldn't find the right value so ordered one I could get. Considering the amount of stress this has put me through all for a 69 cent part, I'm beginning to think I need to seek professional help.
I have checked the voltage across the cat. resistor and am certain of the 32.5v value.

The main issue I think is my old silvertone 6L6gc's. They test very strong so I thought they would be a good choice while I await the JJ's coming wednesday, however, when I test the current on pin three I get 51 mV on one and 63 on the other. I'm thinking they are not well matched (they came out of an old Silvertone 1484 that I'm in the process of rebuilding and since they tested so well I thought I'd pop them in and use them. 

My son is wanting to use this amp when he play in a blues club on thursday and he is pushing for more volume out of the amp.  Compared to my 40 Watt pignose this amp is very quiet and it would be a stretch to play over drums with this amp which suprised us both since it has 2 6V6 power tubes.

Anyway, thanks for your input and concern about my sanity.
Dave
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cmoore
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« Reply #19 on: February 22, 2011, 12:09:19 PM »

Hey Dave....
Help on the forum is free, but my therapy rates are 300 dollars/hour. It is 9AM straight up right now. Shall I start with your obvious hate for your parents.....:-)
Anyway...maybe get some 10 watt resistors ordered for those new JJ's you have coming. BTW, the mA difference you see on your old tubes in not "huge"and may not even be enough to cause any kind of ghosting or any other problem. The benefit of "matched" tubes is still debated. A lot of guys prefer un-matched tubes. Whatever, I think for your purposes, a pair that is within 6 mA will be fine.
If you need something in a hurry, just let me know. I can see what I have and get them in the mail from USA CA 94585. You can send me some replacements when you get a chance. Just an offer. No big deal.
Best...
Chip
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davohilts
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« Reply #20 on: February 22, 2011, 12:45:11 PM »

okay, don't get me started on my parents!
hee, hee!
I am not sure what you mean in regards to the JJ's and my need for 10 Watt resistors! I have ordered some 270 ohm and 300 ohm 10 watters from Mouser and should see them Thursday if all goes well. If you could enlighten me I would be grateful!
Thanks,
Dave
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cmoore
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« Reply #21 on: February 22, 2011, 01:07:31 PM »

Hey Dave -
Sorry about the confisuion.....
Some guys have a long lead time getting parts, depending on where they live and who they order from. I was just offering to mail you a variety of 10 watts until your order arrived. But it sounds like Mouser (I love those guys) has already got you taken care of.
Best
Chip
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wyatt
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« Reply #22 on: February 22, 2011, 09:23:39 PM »

6mA is getting pretty far apart, not a deal breaker with a 6L6GC, but it would be be huge for a 6V6GT or EL84.  These tubes are being biased with the same resistor, so you are talking about one tube burning at nearly10% more dissipation. That's fine if the hotter tube isn't running above 80% dissipation, but rough on the tube if it's not.

As for the tubes testing good...that's a matter of which tube tester and how well it's been calibrated and what that particular manufacturer considered "good."

Wait for the JJ's...and try them with the stock 270 first. 

Also what preamp tubes are you using, the problem may be a preamp tube choking signal off early.

8-ohm speaker, correct?


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davohilts
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« Reply #23 on: February 23, 2011, 10:09:27 AM »

thanks for the input!
8 ohm JBL Speaker
JJ 12AX7 in #2 position
12AY7 6072 box plates 1950s GE-made/say Sylvania in #1 position
I'm hoping the JJ 6L6's come today and the cat. resistor will come tomorrow.
If I want to brighten up the tone a little can I use a 25mf 25 volt cap to bypass the cat resistor?
or if not what might I do to give the amp a little more treble for leads but not lose the nice bottom and mid of the deluxe.
thanks!
Dave
« Last Edit: February 23, 2011, 01:17:15 PM by davohilts » Logged
davohilts
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« Reply #24 on: February 24, 2011, 09:06:11 PM »

got the tubes and resistors and have done the following:
installed 270 ohm cat resister with 22mf 63V cap
installed JJ 6L6 power tubes
replaced the 22mf 40v cap bypassing the 820 resistor on pin 8 of 12AY7 with 2mf 50v cap
replaced the 22mf 40v cap bypassing the 1K5 resistor on pin 3 of 12AX7 with 2mf 50v cap

amp has more bite to it by far and I think when the speaker gets broken in more it will sound fantastic

the tubes are still running at 52 mA each, now balanced but still a little hot.  I might drop in a 300 ohm 10 W cat resistor to see what happens but my son is playing it tonight for the first time!



* 2011-02-21_12-55-23_626.jpg (2241.95 KB, 3264x1840 - viewed 548 times.)
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davohilts
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« Reply #25 on: February 26, 2011, 06:42:37 PM »

Well, Mystery solved!!  It turns out that the newly reconed JBL speaker has a badly rubbing voice coil!  I discovered this when I plugged in a silvertone 1484 twin 12 cabinet to my 4 ohm load jack and the amp sprung to life. OMG the tone is really over the top and the volume is what I was originally expecting.  I then tried a new speaker wire feed to the JBL thinking mine must be defective but still no go.  I pulled the speaker and popped in an old JBL that had a repaired cone tear and fired it up and it sounds even better than I had hoped!
Thanks to all who helped advise, I think the mods I made were great adding some brightness to the tone but it is really a Deluxe on steroids now and my son is in loving the sound!
Dave
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