Classic 30 pre-amp not working

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sagebrother
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Classic 30 pre-amp not working

Post by sagebrother » Thu Dec 27, 2018 8:59 am

I was playing my classic 30 and I wanted to see what it could do so I turned it up quite loud, and i got a loud scratching type sound. I thought maybe I blew a pre-amp tube so i replaced them all. turned it back on and the noise was still there once it warmed up. Ordered some new power tubes, and put them in last night. The pre-amp section does not respond at all. I can plug the guitar in and it will give me some volume. Not a whole lot, but when I try to use the volume controls, clean channel, pre and post, nothing changes. I plugged the guitar into the return of the effects loop and I get the same level of volume. I'm pretty sure I screwed somethng up in the pre-amp section. Are there fuses I could have blown? Reverb hardly works also... you have to turn it up all the way to hardly even hear it.
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Re: Classic 30 pre-amp not working

Post by Classic30inCincy » Thu Dec 27, 2018 11:47 am

How old is the amp ?

It might date back to era with JUMPER CABLE problems !

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JamesPaul
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Re: Classic 30 pre-amp not working

Post by JamesPaul » Thu Dec 27, 2018 4:07 pm

Weak sound from input to speaker would tend to indicate no fuses are blown. Blown fuses typically result in no sound from input to speaker.

Have you sprayed some electronics cleaner on a 1/4 inch plug and worked it in and out of every jack on the amp? Spray the plug before working each jack. This will help if there's dust or corrosion preventing good contact in the jacks.
sagebrother wrote:
Thu Dec 27, 2018 8:59 am
... I plugged the guitar into the return of the effects loop and I get the same level of volume. ...
What level of volume do you get playing thru the effects return? It will not be near as loud as the C30 can get, but it should be loud enough to drown out normal conversation. If it is not this loud, you likely have a power amp section issue. The power section does include V3 in addition to the EL84s, V4-V7.
sagebrother wrote:
Thu Dec 27, 2018 8:59 am
... The pre-amp section does not respond at all. I can plug the guitar in and it will give me some volume. Not a whole lot, but when I try to use the volume controls, clean channel, pre and post, nothing changes. ...
The Normal and Lead channels have different signal paths, but they both go thru V1. So V1 might be wonky, but if you swapped in known good tubes it could be circuit related.
sagebrother wrote:
Thu Dec 27, 2018 8:59 am
... Reverb hardly works also... you have to turn it up all the way to hardly even hear it.
The reverb is in the preamp signal path. Is there any difference in reverb levels between Normal and Lead channels? I'll have to track down a schematic and ponder this a bit.

Did you spray electronics cleaner on the tubes and wiggle (circular motion around the base) them into the socket when you replaced them? This helps if there is dust or corrosion in the sockets.

How easy did the tubes come out and go into the sockets? If it was with very little effort the tube sockets could need retensioned.

Do you have another amp so you could plug the guitar into the C30 input, run out of the C30 effects send into the other amp's effects return? Same sounds from amp number 2 would confirm the C30 preamp issue, but if it sounds normal thru amp number 2 you have narrowed the C30 issue down to the power amp section. You can also reverse this configuration and prove that the C30 power amp is good.

Typically to troubleshoot further than this will require pulling the chassis out of the cabinet. This makes it easy to spray out the pots with electronics cleaner. That is also when you would check for the loose jumper wires Cincy mentions, start checking voltages, tracing signals, etc. If you're pulling the chassis you want to know what you are doing and how to do it safely.
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
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Re: Classic 30 pre-amp not working

Post by JamesPaul » Thu Dec 27, 2018 7:05 pm

Additionally if you have an external cabinet, you could plug it into the extension speaker jack and listen to the external cab. If it sounds normal you may have an issue with the internal speaker.
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
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Re: Classic 30 pre-amp not working

Post by sagebrother » Thu Dec 27, 2018 9:12 pm

I plugged the pre-amp of the C30 into my Special 130's power amp and it was the same... you can talk at a normal volume while hearing the guitar.
I tried the 130's pre-amp into the power amp of the C30 and it worked like it should.

The reverb is extremely weak. If you turn the clean channel volume up all the way you can barely hear it. All the tubes light up. The tag says it is 2004 for manufacture.
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Re: Classic 30 pre-amp not working

Post by sagebrother » Thu Dec 27, 2018 9:31 pm

I found that V-2 was not lit so i put a different tube in there.... I got it to light up, but the volumes still are not good. very quiet and when you turn it all the way up it distorts quietly in the background. when I do the same with the pre and post volumes they distort but they should be blowing my ears out and they do not. it is still very quiet.
My Gear:
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87 MIJ Squire Strat
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Re: Classic 30 pre-amp not working

Post by Classic30inCincy » Thu Dec 27, 2018 10:38 pm

Consider acquiring new pre-amp tubes.

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Re: Classic 30 pre-amp not working

Post by Harry Mowrey » Fri Dec 28, 2018 1:03 pm

Hey,
Before purchasing new tubes pull the preamp tubes one at a time and try them in another amp. If they work in the other amp it's not the tubes. As you pull them, check the tube pins to make sure one did not bend and then not seat properly ( I've had this happen). If the tubes check out then it would be time to start testing signal at the sockets starting with socket #1 if you are comfortable working on an energized board(REMEMBER LETHAL VOLTAGES ARE PRESENT) if not, the time to find a good amp tech is upon you. Good Luck!
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Re: Classic 30 pre-amp not working

Post by sagebrother » Sun Feb 17, 2019 12:30 pm

I swapped out the pre-amp tubes from my triumph, put the tubes from the Classic 30 in and they worked fine... Tubes from the triumph into the classic 30 did not make any difference... Could I have some bad capacitors in the pre-amp section>
My Gear:
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JamesPaul
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Re: Classic 30 pre-amp not working

Post by JamesPaul » Mon Feb 18, 2019 1:26 pm

Tubes are the most likely components to fail, which is why they are in sockets. You have ruled out tubes with your swapping between the C30 and the Triumph.

The next most likely components to fail are power supply related. After those it is the other components in the amplifier. As Cincy already noted, the jumper wires connecting the circuit boards in the Classics can often come loose.

Otherwise the troubleshooting you have completed narrows it down to something in the preamp section. I have owned 2 C20's, 2 C30's & 2 C50's over the past 23 years and cannot say any specific Classic preamp component is prone to failures.

At this point, if it was my C30, I would pull the chassis and start checking the DC voltages. If those are all good I would apply a signal to the input and start tracing it thru the preamp with the o'scope. This should help identify the component that has failed or the jumper that has come loose.

If you are not familiar with safely working on tube amplifiers, please take your C30 to a qualified technician. Voltages stored in tube amplifiers can kill you. Whatever money you might save with the DIY approach is truly insignificant when compared to a human life.
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
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Re: Classic 30 pre-amp not working

Post by sagebrother » Wed Mar 13, 2019 11:05 am

The amp is in the shop as we speak... I will let you know what they find.
My Gear:
PV Triumph 60
PV Bandit 65
Fender Deluxe Reverb Tone Master
Behringer V-Amp Pro
GFS PartsCaster Tele
87 MIJ Squire Strat
2003 Epi Les Paul Custom
2000 Ltd Ed Epi Les Paul Deluxe
Xaviere XV900 335
Xaviere Acoustic/electric

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Re: Classic 30 pre-amp not working

Post by sagebrother » Thu Mar 14, 2019 1:22 pm

They found two broken solder joints... Thanks for all your help guys... Now if only Cincy could message me with his super duper tube recommendations for this beast.
My Gear:
PV Triumph 60
PV Bandit 65
Fender Deluxe Reverb Tone Master
Behringer V-Amp Pro
GFS PartsCaster Tele
87 MIJ Squire Strat
2003 Epi Les Paul Custom
2000 Ltd Ed Epi Les Paul Deluxe
Xaviere XV900 335
Xaviere Acoustic/electric

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Re: Classic 30 pre-amp not working

Post by JamesPaul » Thu Mar 14, 2019 4:32 pm

Great to see this update and that Cincy nailed it right off the top.

When Cincy (and I know he is a busy and very in demand guy) does message you, I think you will find his C30 recommended and PAF tube set is the following.

V1 Tung Sol 12AX7
V2 JJ ECC803S
V3 Sovtek 12AX7LPS

V4-V7 JJ EL84 (breakup tuned to your taste)

I find Cincy's set works quite well in my C50's. Also my C20's, minus the EC803S in the middle and drop the extra EL84s. :wink:
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
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Re: Classic 30 pre-amp not working

Post by Swellsound » Wed Mar 20, 2019 7:07 pm

Have you tried plugging in a patch cable between the effects send and return? If that fixes it, it indicates that the return jack needs to be replaced.

Good luck!

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Re: Classic 30 pre-amp not working

Post by Swellsound » Wed Mar 20, 2019 7:10 pm

Sorry, I just saw your last posts where you mentioned that the shop found a couple of bad solder joints. I would imagine they were probably on the input jack or on the effects loop jacks.

Glad it's fixed!

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