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Groove Tubes Gold Series GT-6V6-C Matched Power Tubes

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I replaced Can I change the tubes on my fender blues deluxe reissue from 6l6 to 6v6 power tubes

An internal component has failed. Without it in front of me for testing I cannot say which. You need to takje it to the repair shop.

Jan 28, 2016 | Fender BLUES-DELUXE-REISSUE Tube Guitar...

1 Answer

What does the CQ or RQ stand for

They are country of origin markers... R is Russia.

Jun 08, 2011 | Groove Tubes GT-6550-CQ Quartet Matched...

1 Answer

I have a peavey valvenmaster head that was playing at very low volumes even when cranked up pretty loudly. i replaced all of the tubes with new matched groove tubes and the volume and tone improved. ...

You start by downloading the schematic here:

Scroll down to the link "Get Manual" and download the schematic. Note that it has several pages of parts list preceeding the schematic.

Next, put a 150 Watt incandescent bulb in series with the power cord to act as a current limiting fuse. Now replace the fuse and proceed with testing. You may find that one or more filter caps have shorted. Also pay particular attention the the BIAS power supply. You should see about -35 to -40 volts. Note that the series lamp will come on if excess current is being drawn and voltages will be low if the lamp lights. If the BIAS supply has failed, it is possible your power tubes have been damaged.

Mar 31, 2011 | Peavey ValveKing 100w All Tube 212 Combo...

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The output is very low and distorted

The problem is very likely a blown tube. You may be able to see which tube is dead by looking in the back of the amp with the room lights turned low and the amp on. If you can that it is one of the four 12AX7 tubes that isn't lighting up, that one should be replaced. If you can see that it is one of the KT66 tubes that isn't lighting up, buy a new matched pair and replace both at the same time.


If all of the tubes are lighting up, then one or more may be bad, but not yet completely dead. Determining the problem would require more testing. If you have one spare, good 12AX7 tube around, try replacing them one at a time and see if that fixes the problem. TURN OFF AND UNPLUG YOUR AMP IN BETWEEN TUBE SWAPS. If a new preamp tube doesn't fix the problem, order a new set of KT66 power tubes and you should be back rocking out in no time.

Mar 06, 2011 | Marshall Amplification Marshall Vintage...

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Laney GH100L amp...weak/distorted output...Output tube plate voltage is 100V higher than the schematic states...any ideas?

That high a voltage MIGHT indicate the output tubes are NOT loading the supply enough. You don't mention the voltages andthe tubes used in the unit. I have a schematic for a AH100 but I don't know if it is close to your unit. That schematic shows four output tubes.
Remember if you put matched tubesas pairs, the pairs need to be on opposite sides of the output transformer.

Feb 16, 2011 | Music

1 Answer

My peavey valveking vk 112 is making a whistling noise I changed the 2 main tubes and it is still doing it what coud be the problem and how can i fix it

A high frequency feedback can be very hard to isolate without test equipment... you MIGHT have a "microphonic" tube that picks up from the speaker and feeds back... Tap the small tubes with a pencil and see if any of them "ring"... gentle taps of course... If one seems sensitive, swap like numbered ones around to see if you can find a happy place for them. Electrically there could be a bad ground inside causing these.
I notice you have 4 tubes in the output... REMEMBER when you used matched pairs... the members of the pairs do NOT go side by side all the way down the string...
Put each tube of a matched pair at the ends of the string of four, and the other pair as the middle two...

Feb 12, 2011 | Peavey ValveKing 100w All Tube 212 Combo...

1 Answer

I was playing through my Jvm410 it was sounding great then the volume got quieter then no sound all lights work whats the problem power tubes maybe?

Yes, you MAY have destroyed the output tubes...

When replacing, make sure your MATCHED pairs go into V1 and V4 and the other into V2 and V3 respectively. Many don't realize the proper placement of matched pairs.

Open unit and if you find the tubes with the plates glowing red OR purple haze down between the elements, the tubes are gonzo.

Check the bias at connector CON1, Between pin 1 and 2 is a 1 ohm resistor in the cathode of the V1 and V2 side. Adjust the Bias1 for the number of milivolts matching the required bias current for two of the output tubes. Do the same for pins 2 and 3 of CON1 for the second side using the BIAS2 control. Fir your amp, you will want each of these set to 70millivolts.

It is possible (hopefully) that one of the smaller tubes burned out. These are much less expensive. EACH of these will have TWO points of light visible when they are operating. If you only see one, then 1/2 may be burned out. When turbes burn out, they cool down and sound will fade out.

There are other components that could cause your problem but those are not DIY unless you are adept at electronics.

Jul 14, 2010 | Marshall MG100HDFX 100-Watt Amplifier Head

1 Answer

No volume.

Are the tubes bad? Do they light up? Check the tubes and install replacements if necessary. If it's a preamp tube that went bad, just replace that one tube. If a power tube went bad then replace the set of power tubes. Be sure to get a matched set when replacing power tubes, and to bias them.

Aug 08, 2009 | Fender Hot Rod Deluxe Guitar Combo...

2 Answers

Turned on switch to crate V33-212 and it shorted out

Your amplifier is a solid-state rectified tube amplifier. This means that a tube is NOT used for the power supply. Why is this significant? Because most of the time you have the problem you are describing, it is because of the tube rectifier.
Since this amp does not have a tube rectifier, the problem is likely one or more of the tubes. I have seen in 95% of the amps I repaired that the tubes were the cause, and since the amp is so new, I would suspect tubes first.
Now the hard part: which tube? Without a tube tester, you will have to use the 'firewall' technique. You will need to get a bunch of replacement fuses, as you might go through a few untill you find the problem. Radio Shack is a great place for fuses (make sure they are SLOW BLOW type).
The problem is almost guarenteed to be the power tubes: they are a big failure mode in tube amps (the preamp tubes are not as likely the problem).

This is what I do at a customer site without a tube tester:
(2) Have plenty of fuses.
(3) Start with power tubes: they cause most of these problems. Replace burned out fuse.
(4) Replace all 2 (or 4 in your case) with the good tubes.
(5) Turn on amp and play on it (30 minutes at various volumes and settings). Turn it on and off many times using the on/off procedure your amp requires (like using the standby switch on some models).

* if the amp plays and works, likely you had a bad power tube. If you are blowing fuses, the problem is either the power amp circuitry or the preamp tubes.

* Leave the good power tubes in before going on to the next step. Also: the minor difference in bias wont matter for what we are doing now: the bias being WAY out is almost never the cause.

(6) Check preamp tubes (easy to do, as this does not require us to poke around on the insides).
(7) Replace burned out fuse (atleast number two by this point).
(8) Replace all preamp tubes.
(9) Turn on and repeat step 5.

* Blowing fuses at this point means atleast two types of repairs needed: retention tube sockets or someone to look inside the amp. Either way, this is a serviceman repair (things I do). Since the amp is so new, take the warentee buyout and throw it back to where you got it. Crate is real good about dealing with these issues (if you are the only owner and it is within warantee).

If you need to contact warantee support, you can tell them you have had the amp re-tubed and the problem still persists (meaning they can brush you off with 'just get it retubed and then call us if there is problems'. This is like 'take two asprins and call me in the morning: 95% of all tube amp problems can be fixed by this (retube, not asprins).

If you have to do the warantee route, KEEP YOUR NEW TUBES. The preamp tubes are fine, but the power tubes may be damaged. Wait for what Crate tells you before you use them. This is if you are cheap. I would pitch all of the tubes and consider the 70 bucks as my cheap attempt to bet I am in the 95% solution number (tubes are the cause). Otherwise, the repair will cost shipping at a minumum. Dont you love it: tube amps are expensive and require someone with deep pockets to enjoy the tone. But what can we do: tubes DO sound better and when everything is working, they perform reasonably well.

Good luck on this!

Mar 24, 2009 | Crate FlexWave FW15 Guitar Amp Combo, 15...

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