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Post by exodus5 on May 6, 2020 19:17:11 GMT -5
I just bought a used Quick Rod that appears to be in really good original condition.
Then amp sounded decent when I tried it out at the seller’s house, but when I got it home and tried it with my cab I realized it wasn’t as defined as I know these amps to be.
It has Mullard EL34s and they are probably a few years old. I hooked up my dual bias probes and the bias jumped up into the 50’s. I verified the plate voltage is 500v, and with 25w tubes At 60% I should be at 35Ma. I adjusted it down to where one tube was around 40 and another was 46Ma. I had adjusted so much to get there that I figured I’d give it a test. Before I made further changes. The sound was so much better. As I sat there playing away and congratulating myself on my work the amp crackled and the sound dropped to almost nothing. I checked the clean channel and same thing. It was like the amp lost 95% of its power. I turned it off and looked for any smoke or obvious issues, but didn’t see anything. I turned the amp back on after disconnecting everything but my guitar and the cab and same thing...once the amp got up to operating temperature the tone was great and then it dies.
Best I can figure I adjusted the bias too low (though it should have been fine at 40) and this caused the issue. I reinstalled my bias probe and adjusted the bias to 44/50Ma and the loss of sound is gone but the tone is worse.
My last idea was to take out the Mullard quartet and install the only other EL34’s I have, a duet of Svetlana tubes, in the two inner sockets. The initial readings for bias on those was in the mid-60’s. What am I missing?
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Post by briman on May 6, 2020 21:00:59 GMT -5
My guess would be defective power tubes. I would put all new tubes in and bias. I had the exact same symptoms you are describing and new tubes solved it.
If that doesn't fix it, then it has bias drift problem which could be caused by bad resistor or solder joint.
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Post by splawndude on May 9, 2020 0:20:01 GMT -5
Did you play the amp with the probe plugged in?
The new/current Mullard power tubes are not the same as the NOS ones.
Turning the bias pot all the way down should not have hurt your amp any.
I'd try the Svetlanas at half power mode as opposed to mixing them.
If you do that turn your ohms down another notch (cut in half).
Best bet like Brian said is get a matched set of new tubes and tell the distributor it is a Splawn and you are looking for something matched in the 35 mA area.
Also try swapping your last 12Ax7 the one in the phase inverter slot.
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Post by exodus5 on May 11, 2020 14:35:02 GMT -5
I was able to get my bias down around 40 average in the “mullard reissue” tubes that were in the amp, but as soon as I put in a new set of Svetlanas the bias was at 62 and I ran out of adjustment at 61Ma. Do I need to find a set of the Russian Mullard Reissues? Will TAD EL34B-STR work? I will look around for a reputable tube seller and see if they know.
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Post by briman on May 11, 2020 20:43:58 GMT -5
I am no amp tech but i think you need to bring it to a tech and check all your resistors etc. One of my marshalls was doing something similar and it was because alot of resistors were changed fro different values when amp was converted to kt66 tubes from el34's and was impossible to bias amp properly until proper resistors put in. I suspect someone has been messing around in your amp.
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Post by splawndude on May 11, 2020 21:46:26 GMT -5
Ask someone for a matched set of power tubes in that 30-40 mA range. If they are tested at that range using a plate voltage of around 475 (sorry 500v in your case) then they should be right there after shipped. If not, then tech time like Brian said and you'll need the power tubes anyway. You shouldn't have to buy any special brand.
Can't speak to the STRs but I think they would be fine. As a matter of fact, I believe Laura from thevalvequeen recommended those to me at one point.
Scott sells tubes too so you could just call him and and explain your situation and have him sell you some.
Doug at Dougs tubes I've found is good and then there is Bob at Eurotubes if you want JJs. Both of those guys (and some others) will actually test and send you tube that will work out of the gate.
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Post by gtrjunior on May 13, 2020 5:56:46 GMT -5
This is what I’ve been Using and is an equivalent to the chinese tubes Scott installs. The price is pretty good although they are a few dollars more than the last time I bought them. (They used to be $13-and change.) But yes, 40mA sounds right. A while back Scott himself told me he biases there. If you have a drop B+ switch, that would then drop the mA to around 30ma when the switch is engaged. Bias with the switch off @ 40mA. www.tubedepot.com/products/sino-el34-b-power-vacuum-tube |
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Post by exodus5 on May 19, 2020 10:10:28 GMT -5
This is what I’ve been Using and is an equivalent to the chinese tubes Scott installs. The price is pretty good although they are a few dollars more than the last time I bought them. (They used to be $13-and change.) But yes, 40mA sounds right. A while back Scott himself told me he biases there. If you have a drop B+ switch, that would then drop the mA to around 30ma when the switch is engaged. Bias with the switch off @ 40mA. www.tubedepot.com/products/sino-el34-b-power-vacuum-tubeThat looks like it might be what I eventually bought. I purchased a quad of TAD EL34B-STRs and I didn’t even have to adjust the bias. Right at 38/39 when installed. I think they are a bit better in the midrange than the Mullards Splawn installed (and noted on a couple labels). I really love the Plexi gear, but any time I use gear 2 I bump up the treble and presence and I need to find a way to tame those gain levels. |
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Post by gtrjunior on May 19, 2020 11:30:35 GMT -5
This is what I’ve been Using and is an equivalent to the chinese tubes Scott installs. The price is pretty good although they are a few dollars more than the last time I bought them. (They used to be $13-and change.) But yes, 40mA sounds right. A while back Scott himself told me he biases there. If you have a drop B+ switch, that would then drop the mA to around 30ma when the switch is engaged. Bias with the switch off @ 40mA. www.tubedepot.com/products/sino-el34-b-power-vacuum-tubeThat looks like it might be what I eventually bought. I purchased a quad of TAD EL34B-STRs and I didn’t even have to adjust the bias. Right at 38/39 when installed. I think they are a bit better in the midrange than the Mullards Splawn installed (and noted on a couple labels). I really love the Plexi gear, but any time I use gear 2 I bump up the treble and presence and I need to find a way to tame those gain levels. A while back I had put a set of Mullard RI in mine too. Holy midrange....way too much for me. My guess is that the guy you bought the amp from put them in. AFAIK, Scott has never used them. Of course, I could be wrong but I’d be surprised if they are factory installed. And yes, gear 2 can be hard to control at times. Do you have the loop volume feature? |
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Post by exodus5 on May 19, 2020 13:29:27 GMT -5
That looks like it might be what I eventually bought. I purchased a quad of TAD EL34B-STRs and I didn’t even have to adjust the bias. Right at 38/39 when installed. I think they are a bit better in the midrange than the Mullards Splawn installed (and noted on a couple labels). I really love the Plexi gear, but any time I use gear 2 I bump up the treble and presence and I need to find a way to tame those gain levels. A while back I had put a set of Mullard RI in mine too. Holy midrange....way too much for me. My guess is that the guy you bought the amp from put them in. AFAIK, Scott has never used them. Of course, I could be wrong but I’d be surprised if they are factory installed. And yes, gear 2 can be hard to control at times. Do you have the loop volume feature? No. My Quickrod is (I believe) a 2006 and just has the in/out and “level” & “bypassed” switches. I just bought a Rivera Rockcrusher so I can try to keep the windows from breaking. I am now looking at my cab (4x12 creamback loaded Marshall 1960a) to see if doing an X-pattern with some greenbacks/smallblocks/v30’s will help the note definition at higher gain. |
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Post by gtrjunior on May 19, 2020 15:52:20 GMT -5
I’m not a fan of the V30 with this amp, although others may like them. I think the creamback/small blocks are a great idea.
I have also found that I like a 250K volume pot on my bridge humbucker. I still prefer the 500K for the neck pickup though.
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Post by exodus5 on May 19, 2020 19:56:14 GMT -5
I called and spoke to (I assume) Scott directly today when I decided to buy a pair of small blocks to add to my cabinet. He told me that the small blocks are actually pretty much the same thing (close enough, at least) and it wouldn't be a discernable difference. He did reiterate that the V30's would not sound good with the amp. His recommendation was to paid a set of Creamback "H's" with my "M's". I had already ordered a v30, so I'll give that a try before ordering anything else, but if the v30 really doesn't sound good I will try the different rating of Creambacks.
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Post by splawndude on Jun 2, 2020 23:07:26 GMT -5
Let us know.
I bet that was Scott.
Makes sense on the Creambacks.
See what you think about the V30s (in a X pattern?)
I like the H and M combo idea.
I also hear Eminence Legends are a good match to mix in
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Post by briman on Jun 3, 2020 5:57:55 GMT -5
I had an H and an M paired in a 2x12 with my QR and sounded great. Very smooth rounded top end. Now i have them in a 4x12 with 2 other greenbacks. It sounds incredible. Greenbacks add a little more bite.
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