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Hey all....so I have this Carvin Valvemaster on the bench... like.it says, even on the clean channel, it is very quiet and distorted. I tested the power tubes and preamp tubes with my Superior tube tester...I found.1 preamp tube to be in the "replace" zone of the meter....no joy. I plugged the guitar directly into the effects return and it is still low volume and distorted so I'm pretty sure I can rule out the preamp. Anybody ever have any issues like this? Thanks for looking! I love and appreciate you guys!!!!!
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It's time to start checking power supply voltages in the power amp circuit. Do you have a schematic? -
Check the anode voltages, we are looking for a high value anode load resistor. Are the G2 voltages correct on the EL34s?Support for Fender, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
If you can't fix it, I probably can.Comment
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Support for Fender, Laney, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk
If you can't fix it, I probably can.Comment
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Thank you for the replies! The guy has 6L6s in the amp. I did find a schematic...I will be able to take voltage measurements after 2:30 as I'm at my day job.Comment
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Does this amp have those notorious gray flat ribbon cables with plug/pin ends? If so, pull every one and clean the plugs and pins with something you know works. I use DeoxIT D-series in the little bottle. Those cables caused more than their share of problems in the later Carvin models.Comment
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It only has a single 4 conductor ribbon-type cable that goes from the effects loop to the main board... it's an older amp. Date says 10/95... and there are no connector ends. All wires are hard soldered to the boards...Comment
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A parasitic oscillation can sound like that.Comment
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In theory, plugging into the effects return should eliminate the shorting phone jack as a problem, but it would be a quick test to connect the send and return jacks with an instrument cable and see what the amp does with the guitar plugged into the normal input. The (low) input impedance and (low) input sensitivity of the effects return stage aren’t really a great match for a guitar, unless it was an acoustic with a built-in preamp, or you used an external preamp between the guitar and the effects return. However, you did say the sound was still distorted when you did your test, so maybe that shorting jack is okay. Still, it’s only a one-minute test, so I think it falls into the “why not try it” category.
Can you contact the client and ask what the circumstances of the failure were? Did it fail during a show? Did it fail right after load-in? Did it fail when he got it home after a show? Was it bumped? Did anyone else handle the amp? Was the amp loaned out and it came back broken? Was it run without a speaker load? (According to the Rev G schematic, the speaker out phone jacks are not shorting jacks.) Did someone trip over the speaker cable while the amp was in use and the player kept playing while he (or someone else) was trying to figure out what was wrong? The more info from the owner, and the more detailed, the better.
If this amp travels a lot, could be something as simple as a flaky solder joint, and all it would take is a slight bump (or a 100th bump) to crack it free. Also if the owner started moving tubes around before he brought the amp to you, especially if he rocked the tubes back and forth, that might have cracked a solder joint at a tube socket pin. (I assume the sockets are PCB-mounted. If not, then disregard.)
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Thank you NHBASSGUITAR... I had done everything you said in your post....EXCEPT shorting the effects loop....surely it wont work as I already plugged into the effects return and it still sounded like shite, right? WRONG! It most certainly brought the full signal back! I blasted it with some Deoxit and inserted a 1/4" Jack into it multiple times....gonna do it again when I get home too... man its funny how many simple things one disregards only to find out that is actually what it was...lol! Once again, thank you sir....and normally that is one of the first things I do to an amp with a weak signal....wow....Comment
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Out of curiosity, if you have a chance, plug your guitar into the FX return jack again now that it's working right. Does it now sound same or different?Originally posted by Enzo
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I will certainly do that when I get home. I am curious about that myself... I was running late this morning and I didn't have time to grab the amp chassis on my way out the door. Lol!Originally posted by g1 View PostComment
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Glad it was a simple fix.Originally posted by Danglin' Fury View Post
I have an Aguilar TH500 with a notoriously troublesome effects return jack. Whenever I use the amp, I patch the send to the return. Always. I don't even bother checking any more whether the return jack's shorting contacts will close reliably. I just assume they're not going to. Maybe one day I'll dig into it, but it's at the very bottom of my Meh List, so it probably won't be soon.Comment
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