It is currently Mon Mar 16, 2020 11:10 pm

All times are UTC - 7 hours



Post new topic Reply to topic  [ 100 posts ]  Go to page Previous  1, 2, 3, 4, 5 ... 7  Next
Go to page Previous  1, 2, 3, 4, 5 ... 7  Next
Author Message
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 2:56 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Max tube watt rating times 50% to 70%, divided by the Plate volts equals the current for one tube. The test point is for two tubes. The test point mV can be directly translated to mA, use the terms interchangeably.

30 watt tube times 50% to 70% equals 15 watts to 21 watts. 15 watts divided by 430 Plate volts equals about 35 mA (times two for both tubes equals 70 mA at test point). 21 watts divided by 430 Plate volts equals about 49 mA (times two for both tubes equals 98 mA at test point). 430 Plate volts used for reference only, measure to be sure, remeasure and recalculate after any adjustment.

So, a decent range to shoot for at the test point would be between 70 mV and 98 mV, assuming approx 430 Plate volts.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Fender Play Winter Sale 2020
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 3:04 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
shimmilou wrote:
Max tube watt rating times 50% to 70%, divided by the Plate volts equals the current for one tube. The test point is for two tubes. The test point mV can be directly translated to mA, use the terms interchangeably.

30 watt tube times 50% to 70% equals 15 watts to 21 watts. 15 watts divided by 430 Plate volts equals about 35 mA (times two for both tubes equals 70 mA at test point). 21 watts divided by 430 Plate volts equals about 49 mA (times two for both tubes equals 98 mA at test point). 430 Plate volts used for reference only, measure to be sure, remeasure and recalculate after any adjustment.

So, a decent range to shoot for at the test point would be between 70 mV and 98 mV, assuming approx 430 Plate volts.


BINGO! :mrgreen:

Also, refer to this thread:

viewtopic.php?f=13&t=88475

_________________
Bill

Image


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 3:06 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
bluesky636 wrote:
...I really don't care about the tube's rating...


It has to do with the amp volume level at which breakup starts to occur. Similarly biased tubes with different ratings will have different breakup points. For example, all other things being equal in the same amp, a tube rated at 20 (Ip) compared to a tube rated 40 (Ip), both biased at say 35 mA, the lower rated tube will begin to breakup at a much lower volume level than the one with the higher rating. You can get a bit more output/headroom from the amp using the higher rated tubes.

Of course I have a feeling that like me, you probably keep your amps at a fairly low volume, so the rating might not be as important. Or is it that we have to turn them up louder to be able to hear them......I can't remember. :lol:

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 3:37 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
shimmilou wrote:
bluesky636 wrote:
...I really don't care about the tube's rating...


It has to do with the amp volume level at which breakup starts to occur. Similarly biased tubes with different ratings will have different breakup points. For example, all other things being equal in the same amp, a tube rated at 20 (Ip) compared to a tube rated 40 (Ip), both biased at say 35 mA, the lower rated tube will begin to breakup at a much lower volume level than the one with the higher rating. You can get a bit more output/headroom from the amp using the higher rated tubes.

Of course I have a feeling that like me, you probably keep your amps at a fairly low volume, so the rating might not be as important. Or is it that we have to turn them up louder to be able to hear them......I can't remember. :lol:


WHAT? I can't hear you!

Not sure that I agree (though I'm not sure how to prove it).

You are only considering plate current, but what is the plate voltage at that current rating? Seems to me that the percentage of max plate dissipation that the two example tubes are biased at is the determining factor of when they break up. If the lower rated tube is biased at 70% and the higher rated tube is biased at 70%, both plate current and plate voltage will be different, but both tubes will still be putting out about 21 watts at idle (for a 6L6GC). I think the rating is only a concern for non-adjustable fixed bias amps like early Blues Deluxes/Devilles (I think the Hot Rods were always adjustable, right?) and Mesas.

Like I said, I have never ordered tube based on their ratings. I just bias them up to about 70% and wail! :lol: :lol: :lol:

_________________
Bill

Image


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 3:57 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Wed Mar 31, 2010 12:48 am
Posts: 26417
Location: Tombstone Territory
Funny thing about those "ratings"......the finest 6L6GC's ever made or ever to be made in the entire history of mankind on planet Earth had no such arbitrary grading.

(of course I'm referring to my beloved blackplate RCA's)

:mrgreen:

Arjay

_________________
"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 4:11 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
Retroverbial wrote:
Funny thing about those "ratings"......the finest 6L6GC's ever made or ever to be made in the entire history of mankind on planet Earth had no such arbitrary grading.

(of course I'm referring to my beloved blackplate RCA's)

:mrgreen:

Arjay


Right. Bias them up and BANG! You're done.

_________________
Bill

Image


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 4:14 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Sun Aug 05, 2012 9:50 am
Posts: 1399
shimmilou wrote:
Max tube watt rating times 50% to 70%, divided by the Plate volts equals the current for one tube. The test point is for two tubes. The test point mV can be directly translated to mA, use the terms interchangeably.

30 watt tube times 50% to 70% equals 15 watts to 21 watts. 15 watts divided by 430 Plate volts equals about 35 mA (times two for both tubes equals 70 mA at test point). 21 watts divided by 430 Plate volts equals about 49 mA (times two for both tubes equals 98 mA at test point). 430 Plate volts used for reference only, measure to be sure, remeasure and recalculate after any adjustment.

So, a decent range to shoot for at the test point would be between 70 mV and 98 mV, assuming approx 430 Plate volts.


Here is where some fuzziness creeps in for me. mA and mV. The multimeter I have can offers mA reading but I do not see a setting for mV. When I went for a reading in my HRDIII the other day, I got 25 mA. One of the tubes would not glow bluish when I played. Switched tubes into other sockets. Same tube glowed bluish while the other didn't again.

Question. Do I have a deadish tube? 25mA sounds like half of a pretty cold bias setting. New tubes came today, but they are a half mile away in a mailbox with 6 inches of snow on the ground and more falling. I am wondering if tubes are why I got the very low bias reading.

The amp sounds good. :D

_________________
I have some Fender gear.
(Telecaster, Jaguar, Villager 12 String. Mustang l, Bronco, SCX2, Rumble 350, HRDIII, Rumble 2x8 Neo Cab)
http://www.reverbnation.com/modwiz


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 4:37 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
modwiz wrote:
Here is where some fuzziness creeps in for me. mA and mV. The multimeter I have can offers mA reading but I do not see a setting for mV. When I went for a reading in my HRDIII the other day, I got 25 mA. One of the tubes would not glow bluish when I played. Switched tubes into other sockets. Same tube glowed bluish while the other didn't again.

Question. Do I have a deadish tube? 25mA sounds like half of a pretty cold bias setting. New tubes came today, but they are a half mile away in a mailbox with 6 inches of snow on the ground and more falling. I am wondering if tubes are why I got the very low bias reading.

The amp sounds good. :D


There is no way that you can read mA directly on any Hot Rod amp without breaking the connection between the cathode and ground or the plate and the transformer and inserting the meter in line. If you are using the Fender test point, you are measuring across a one-ohm resistor inserted in the cathode circuit of the power tubes and the meter must be set to the lowest voltage scale. If you are reading 60 mV (the Fender spec) across the one-ohm resistor, Ohm's law says you are reading 60 mA total or 30 mA per tube.

_________________
Bill

Image


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 4:42 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
Retroverbial wrote:
Funny thing about those "ratings"......the finest 6L6GC's ever made or ever to be made in the entire history of mankind on planet Earth had no such arbitrary grading.

(of course I'm referring to my beloved blackplate RCA's)

:mrgreen:

Arjay


Not arbitrary, there have always been specs for tubes, see the data sheet, it gives the grid voltage, Plate current, trans-conductance, etc.

Oh, the tubes varied as far as specs, but those specs were probably tighter back then. If you did get out-of-spec tubes most people wouldn't know since not many bothered to check them. Hopefully we are a bit wiser these days about biasing. I think that our memories (what's left of them) can be a bit selective about "the good old days" when everything was just peachy. :wink:

A given tube will draw X amount of Plate current at Y grid voltage with Z Plate volts. Using the same grid voltage and Plate voltage in an amp, if two tubes have two different Plate currents, that means that you would have to increase the grid voltage on one tube to match the Plate current of the two tubes, and that means that the increased grid voltage will change the way that the tube conducts when an AC signal (guitar) is applied, resulting in a different onset of breakup for one tube vs the other. So, biasing the differently rated tubes to the same Plate current and Plate voltage requires a different grid voltage for each tube, and as we know, the grid voltage is "wiggled" by the applied AC signal from the guitar.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 4:51 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
modwiz wrote:
...The multimeter I have can offers mA reading but I do not see a setting for mV....


The lowest VDC scale will work, you just have to translate to mV. If you read .065 VDC, that is 65 mV.

+1 to what bluesky636 posted about using the multimeter.

If you read 25 mA, that was probably roughly about half, as the shunt in the meter is conducting part of the current, and the one ohm resistor at the amp test point is conducting part of the current.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 4:58 pm
Offline
Hobbyist
Hobbyist
User avatar

Joined: Mon Dec 30, 2013 8:59 am
Posts: 14
Location: Italy
wow a lot of answers!
But I'm sorry if I ask it again.. what if I put my GT 6L6S's tubes (now at 60mA) at bias 45 mA? they will die or something like this?
bluesky said that if I bias down my 6L6S I will get more headroom..
shimmilou said that 70 mA (according to plate volt) si considered 'cold bias', or have I misunderstood you? I'm sorry if I did it..

I'm a little lost..

If I buy 6L6R I'm sure of the rating but not for the harmonic sound
If I buy 6L6GC JJ I'm sure of The harmonics sound but I can fine them too early in break up..
what should I do? damn I'm in Italy.. I wish to live in USA :(

thanks a lot guys and I'm so sorry if I don't understand all The help you are givin to me..

_________________
The Guitarist


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 5:09 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
If you bias your tubes too low, you might get a nasty sound (crossover distortion), and if you bias too high you might get shorter tube life. That's why we advise the general 50% to 70% range, so the tubes will be hot enough to sound good, but not so hot as to prematurely shorten the life. Within that range, set for more or less headroom, considering tube life. IMO, 70 mV is as low as the bias should be set, and if memory serves, mine is somewhere around 75 mV to 80 mV at the test point. Actually, I set the bias using bias probes, a little more accurate, and I can check the matching of the tubes.

You have a good point about the GT Rs, they could be considered a bit sterile, not as musically rich in harmonics as some other tubes.

What should you do? My advice, pay the price and get the tubes that will make you happy, set the bias carefully to insure long tube life, and enjoy.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 5:22 pm
Offline
Professional Musician
Professional Musician
User avatar

Joined: Sun Aug 05, 2012 9:50 am
Posts: 1399
shimmilou wrote:
modwiz wrote:
...The multimeter I have can offers mA reading but I do not see a setting for mV....


The lowest VDC scale will work, you just have to translate to mV. If you read .065 VDC, that is 65 mV.

+1 to what bluesky636 posted about using the multimeter.

If you read 25 mA, that was probably roughly about half, as the shunt in the meter is conducting part of the current, and the one ohm resistor at the amp test point is conducting part of the current.


Apologies if I seem slow. I have the multimeter see at 200 mA. Is this the correct setting? Thanks to all answering.

I will be making a trip to my mailbox and will be getting new TS 5881's to put in there. Oh yes, two different 12at7's to try in V3. A TS 12at7w and a Jan-Phillips 12 at7wc.

_________________
I have some Fender gear.
(Telecaster, Jaguar, Villager 12 String. Mustang l, Bronco, SCX2, Rumble 350, HRDIII, Rumble 2x8 Neo Cab)
http://www.reverbnation.com/modwiz


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 5:31 pm
Offline
Rock Icon
Rock Icon
User avatar

Joined: Tue Jun 29, 2010 1:20 pm
Posts: 9640
Location: Indiana
No. Use the lowest VDC scale. If using the test point to set the bias, you want to read the voltage drop across the provided one ohm resistor. Without a long explanation of Ohm's law, in the case of this amp's bias test point, the mV reading can be directly translated to mA. In other words, 70 mV at the test point (.070 VDC) is 70 mA of current through both output tubes, 35 mA each tube. Ohms law: E = I x R, where E is voltage, I is current and R is resistance.

_________________
---> "The amp should be SWITCHED OFF AND UNPLUGGED before you do this!" <---

Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


Top
Profile
Post subject: Re: Tubes for Hot Rod Deluxe III for max headroom?
Posted: Thu Jan 02, 2014 5:43 pm
Offline
Rock Star
Rock Star

Joined: Mon Apr 05, 2010 2:37 pm
Posts: 8708
Location: Natural Bridge, Virginia
modwiz wrote:
Apologies if I seem slow. I have the multimeter see at 200 mA. Is this the correct setting? Thanks to all answering.


Repeating what I wrote earlier:

bluesky636 wrote:
There is no way that you can read mA directly on any Hot Rod amp without breaking the connection between the cathode and ground or the plate and the transformer and inserting the meter in line. If you are using the Fender test point, you are measuring across a one-ohm resistor inserted in the cathode circuit of the power tubes and the meter must be set to the lowest voltage scale. If you are reading 60 mV (the Fender spec) across the one-ohm resistor, Ohm's law says you are reading 60 mA total or 30 mA per tube.

_________________
Bill

Image


Top
Profile
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 100 posts ]  Go to page Previous  1, 2, 3, 4, 5 ... 7  Next
Go to page Previous  1, 2, 3, 4, 5 ... 7  Next

All times are UTC - 7 hours

Fender Play Winter Sale 2020

Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to: