Chad
Slender Hobbit
Except for the Nomad 65 and the dirty channel on the Hot Rod Deluxe, all of them sounded great. I would love to have all of them again except the Nomad, that thing was a turd.
Question: How bad an idea is this?
- Thread starter cvogue
- Start date
Except for the Nomad 65 and the dirty channel on the Hot Rod Deluxe, all of them sounded great. I would love to have all of them again except the Nomad, that thing was a turd.
cvogue
Yes, that's Oolong. :)
OK, so here's the scoop.
I'm only half foolish...
So I took the tubes and my multimeter to practice and I swapped them in. I didn't really have time to tear the amp apart to bias (it's not trivial with a Blackstar) so kept an eye on the tubes and the temperature of the amp as well as my ears to see if anything was amiss.
Went well, practiced for a couple of hours, sounded good and I was pleased, more on that in a minute.
So that was yesterday. Today I tore the amp apart... with Blackstars you have to remove the amp from the chassis and then there are a couple of test points that you have to check while changing the bias adjustment pot. It was running hot (supposed to be 50 mA and it was over 60) but not terribly so. I backed it down to just about 50 and called it good. Interesting that a little adjustment goes a long way. I turned the adjustment screw about a turn and it went all the way down into the 30's, took a bit of trial and error and I got it to 50.
Biasing was easy once the thing was torn apart. Biggest pain was getting the amp back into the chassis by myself and getting the screws to thread to tighten it down.
Now I know what you all are thinking... "Yeah great cvogue, you didn't fry your amp, good for you.... now how did the Tung Sols sound?!?!?!?!"
They sound good, actually quite different from the TADs that were in there. The TS's are brighter and have more punch, but not as smooth. The first song we did was "Running Down a Dream" by Tom Petty and the other guitar player said that the solo sounded awesome! More organic (less sterile) sounding than the TADs. He was a bit bummed since now my Blackstar sounds a lot more like his JCM800, heh-heh! It is brighter, more articulate and punchier. I like it. I swear these tubes don't break up as much as the TADs, Seems like I need the gain increased a bit to get there but it's all good.
One thing I found interesting, I could get those elusive 4th fret harmonics more easily (actuall all the harmonics were easier) with the Tung Sols.
So there ya go. Opinions? Questions? Comments? Bring 'em on!
Oh, one question I had... pulling the TADs out took a lot of effort, putting the TS's in was easy, but they seem a bit loose. The spring tube "keepers" work great though. Could I have messed up a socket or is that something to not worry about, the TS's are slimmer than the TADs
I'm only half foolish...
So I took the tubes and my multimeter to practice and I swapped them in. I didn't really have time to tear the amp apart to bias (it's not trivial with a Blackstar) so kept an eye on the tubes and the temperature of the amp as well as my ears to see if anything was amiss.
Went well, practiced for a couple of hours, sounded good and I was pleased, more on that in a minute.
So that was yesterday. Today I tore the amp apart... with Blackstars you have to remove the amp from the chassis and then there are a couple of test points that you have to check while changing the bias adjustment pot. It was running hot (supposed to be 50 mA and it was over 60) but not terribly so. I backed it down to just about 50 and called it good. Interesting that a little adjustment goes a long way. I turned the adjustment screw about a turn and it went all the way down into the 30's, took a bit of trial and error and I got it to 50.
Biasing was easy once the thing was torn apart. Biggest pain was getting the amp back into the chassis by myself and getting the screws to thread to tighten it down.
Now I know what you all are thinking... "Yeah great cvogue, you didn't fry your amp, good for you.... now how did the Tung Sols sound?!?!?!?!"
They sound good, actually quite different from the TADs that were in there. The TS's are brighter and have more punch, but not as smooth. The first song we did was "Running Down a Dream" by Tom Petty and the other guitar player said that the solo sounded awesome! More organic (less sterile) sounding than the TADs. He was a bit bummed since now my Blackstar sounds a lot more like his JCM800, heh-heh! It is brighter, more articulate and punchier. I like it. I swear these tubes don't break up as much as the TADs, Seems like I need the gain increased a bit to get there but it's all good.
One thing I found interesting, I could get those elusive 4th fret harmonics more easily (actuall all the harmonics were easier) with the Tung Sols.
So there ya go. Opinions? Questions? Comments? Bring 'em on!
Oh, one question I had... pulling the TADs out took a lot of effort, putting the TS's in was easy, but they seem a bit loose. The spring tube "keepers" work great though. Could I have messed up a socket or is that something to not worry about, the TS's are slimmer than the TADs
gtrjunior
Wannabe
The pins on TAD seem slightly larger so that's maybe why the TS slid in easier...
Question: when you replaced/biased the new set of tubes, what was your plate voltage reading? 50mA seems really hot to me. But I've never owned a Blackstar so...
My QR biases up around 35mA and my JCM 800 slightly higher. That's at a 70% dissipation.
Question: when you replaced/biased the new set of tubes, what was your plate voltage reading? 50mA seems really hot to me. But I've never owned a Blackstar so...
My QR biases up around 35mA and my JCM 800 slightly higher. That's at a 70% dissipation.
cvogue
Yes, that's Oolong. :)
Didn't measure the plate voltage (didn't know to do that, newb here...) Basically I saw "50mV" silkscreened between the two test points (TP10 and TP18) and I measured that voltage and adjusted the bias pot (see image below) until it read 50 mV...
I'm not sure what that voltage between the test points really represents... I'm thinking it involves both tubes, (each tube was marked 25 mV, so that jibes well with the 50mV value but maybe I'm missing something).
wagdog
Ack
You can measure plate voltage off the board if that trace is connected to the plate. Or, you can measure off the pin the plate is plugged into. Warning: it's going to be upwards of 400 or more volts. Don't screw around with it unless you know what you're doing.
If your amp is like pretty much every other amp with a bias test point, the test point where you measured 50mv is a 1 ohm resistor between the cathode and ground. You're actually measuring the voltage drop across that resistor, but since the resistor is 1 ohm, it has a 1->1 ratio with current.
Do you have a schematic for the amp?
If your amp is like pretty much every other amp with a bias test point, the test point where you measured 50mv is a 1 ohm resistor between the cathode and ground. You're actually measuring the voltage drop across that resistor, but since the resistor is 1 ohm, it has a 1->1 ratio with current.
Do you have a schematic for the amp?
wagdog
Ack
Question: Is that test point running both cathodes through it? If so, you would divide the current by 2 to get the current for each tube (provided a matching set).
cvogue
Yes, that's Oolong. :)
That's what I'm thinking, each tube was rated at 25 mV (according to the markings on the tubes) so 50mV makes sense. Although I think it's a bit of luck that it worked out that perfectly. Tube Depot certainly didn't know they were going into a Blackstar HT-40!
Edit: Don't have a schematic and haven't been able to track one down... will keep looking.
Last edited:
gtrjunior
Wannabe
I don't think so,however I'm not a tech so I can't say for certain. I CAN tell you this:
I bias my amp with a bias probe that plugs directly into the tube socket and then the tube plugs into that. It gives me a plate voltage readout for the entire compliment of tube regardless of the number of them. (My JCM 800 is a 50w and my Quickrod is a 100w)
Both of those amps have only 1 bias point to adjust the entire set(or quad) of tubes.
Before I bought my probe, a friend used to bias my amps for me. He had tried to reach me a one time but it escaped me...I do however remember that he measured the plate voltage from only 1 tube with his multimeter.
Not sure if that answered your question or not but you may be able to google it or look up a YouTube vid explaining the process...you may get a better answer that way
I bias my amp with a bias probe that plugs directly into the tube socket and then the tube plugs into that. It gives me a plate voltage readout for the entire compliment of tube regardless of the number of them. (My JCM 800 is a 50w and my Quickrod is a 100w)
Both of those amps have only 1 bias point to adjust the entire set(or quad) of tubes.
Before I bought my probe, a friend used to bias my amps for me. He had tried to reach me a one time but it escaped me...I do however remember that he measured the plate voltage from only 1 tube with his multimeter.
Not sure if that answered your question or not but you may be able to google it or look up a YouTube vid explaining the process...you may get a better answer that way
wagdog
Ack
Not to quibble, but, a bias probe in a tube socket will give the plate voltage for that half of the OT. The other side may have a slightly different plate voltage - it won't be off enough to matter unless something is out of whack with the OT.
I'm a fan of bias probes myself, it's an easier way to get a quick picture without disassembly.
Usually the bias test point has all of the cathodes tied together and running through a single 1 ohm resistor. The voltage (directly converted to current) is then cummalative. I do seem to remember seeing an amp with two bias test points though... I think it was a Marshall.
@cvogue - the 25mv marked on the tube is half the story; you need to know at what voltage they measured it. They mark them for matching purposes.
I'm a fan of bias probes myself, it's an easier way to get a quick picture without disassembly.
Usually the bias test point has all of the cathodes tied together and running through a single 1 ohm resistor. The voltage (directly converted to current) is then cummalative. I do seem to remember seeing an amp with two bias test points though... I think it was a Marshall.
@cvogue - the 25mv marked on the tube is half the story; you need to know at what voltage they measured it. They mark them for matching purposes.
gtrjunior
Wannabe
Correct about the probe....what I do is measure the plate voltage of both sets. In the QR the 2 inner work together and the 2 outer work together. The reading is always very close. Close enough to not really worry about compensating for. There would have to be quite a large discrepancy to have the need to readjust the bias.
I'm not sure about theQR but a previous owner of my JCM installed the 1 ohm resistor so yeah, it makes it easier to read with the multimeter.
And yes, there are some amps with more than 1 bias point. I was just referring to my 2 amps having 1.
I'm not sure about theQR but a previous owner of my JCM installed the 1 ohm resistor so yeah, it makes it easier to read with the multimeter.
And yes, there are some amps with more than 1 bias point. I was just referring to my 2 amps having 1.