[Drakelist] L-4B reduced power
Garey, Hi... I was just reading a post you made on reduced drive to the L-4B from the T-4any. You mentioned having the load at 0. Are you talking the T-4any or the L-4B as to the loading on 0...I suspect it is the T-4any. What if we load up the T-4any to a lower power out by putting the loading somewhere in between 0 and the max smoke position?? Are RF attenuators available somewhere? If this is the preferred way to do it? Who know...I might want to use my Alphs 91B with the T-4any? In that case I need 5-30 watts of drive. Thanks, Lee ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] L-4B reduced power
I have this problem with my vintage AM station, I use a Yaesu FL2100B with a Johnson Viking-II and to lower the drive level I use a coaxual T placing a dummy load on the T and continue the coax to the anplifier. - Original Message - From: drakelist-boun...@zerobeat.net drakelist-boun...@zerobeat.net To: drakelist@zerobeat.net drakelist@zerobeat.net Sent: Tue Apr 26 07:37:31 2011 Subject: [Drakelist] L-4B reduced power Garey, Hi... I was just reading a post you made on reduced drive to the L-4B from the T-4any. You mentioned having the load at 0. Are you talking the T-4any or the L-4B as to the loading on 0...I suspect it is the T-4any. What if we load up the T-4any to a lower power out by putting the loading somewhere in between 0 and the max smoke position?? Are RF attenuators available somewhere? If this is the preferred way to do it? Who know...I might want to use my Alphs 91B with the T-4any? In that case I need 5-30 watts of drive. Thanks, Lee ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] L-4B reduced power
John, So what is the details of this setup? How much power goes to the amp, with the dummy load in the circuit? My Alpha only need 35 - 40 watts drive to put out 1500. I usually like to run it with 25 watts drive. Also, I don't want to run my L-4B at full throttle either (800-1,000 out) 73, Lee -Original Message- From: John Hudson john.hud...@calema.ca.gov To: 'kc9...@aol.com' kc9...@aol.com; 'drakelist@zerobeat.net' drakelist@zerobeat.net Sent: Tue, Apr 26, 2011 11:24 am Subject: Re: [Drakelist] L-4B reduced power I have this problem with my vintage AM station, I use a Yaesu FL2100B with a Johnson Viking-II and to lower the drive level I use a coaxual T placing a dummy load on the T and continue the coax to the anplifier. - Original Message - From: drakelist-boun...@zerobeat.net drakelist-boun...@zerobeat.net To: drakelist@zerobeat.net drakelist@zerobeat.net Sent: Tue Apr 26 07:37:31 2011 Subject: [Drakelist] L-4B reduced power Garey, Hi... I was just reading a post you made on reduced drive to the L-4B from the T-4any. You mentioned having the load at 0. Are you talking the T-4any or the L-4B as to the loading on 0...I suspect it is the T-4any. What if we load up the T-4any to a lower power out by putting the loading somewhere in between 0 and the max smoke position?? Are RF attenuators available somewhere? If this is the preferred way to do it? Who know...I might want to use my Alphs 91B with the T-4any? In that case I need 5-30 watts of drive. Thanks, Lee ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] L-4B reduced power
This is just my own experience running a T4x into a KW linear that needed 30W of drive (pair of 4cx300 grid driven) While the T4 loading control will reduce the output, it tends to make the output non-linear from the T4X. It is better, signal quality wise, to tune the load control properly and back off the power using the RF Gain control. In order to keep the gain control in a reasonable range, I used a 3dB attenuator in a small box in between the T4X and the Amp. This was a simple device made up of a TEE network of Ohmite non-inductive resistors. Use the formula for resistive attenuators for values. Very small, monolithic attenuators are now available from the likes of Anaren, and can be mounted on a small heatsink and work beautifully also. Sometimes available on auction for cheap. Still a good idea to use a monitor scope to be certain that everything is running in a linear manner. Loading and mismatch of T4x output and the Amp input can lead to much distortion and be non-apparent by viewing meters. FWIW Curt KU8L kc9...@aol.com wrote: Garey, Hi... I was just reading a post you made on reduced drive to the L-4B from the T-4any. You mentioned having the load at 0. Are you talking the T-4any or the L-4B as to the loading on 0...I suspect it is the T-4any. What if we load up the T-4any to a lower power out by putting the loading somewhere in between 0 and the max smoke position?? Are RF attenuators available somewhere? If this is the preferred way to do it? Who know...I might want to use my Alphs 91B with the T-4any? In that case I need 5-30 watts of drive. Thanks, Lee ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] L-4B reduced power
Curt - That is yet another way. I'm not sure why using reduced loading would make the output non-linear It's a 'linear' amplifier which implies that it's 'linear' from zero to full output. It may be that one of the lower level stages are distorting, but I'm not sure why they would. Using the Mic GAIN to reduce output is ok, but you begin to run into S/N problems in the AF and BAL MOD stages. Your three dB pad would certainly help in that regard. Of course you always have the 'possibility' that the MIC GAIN gets left too high from barefoot operation or other accident which would probably blow the grids, (but perhaps not.) Obviously the 3 dB pad has to dissipate whatever power is not fed through to the amplifier. Short duty cycle of SSB might help somewhat, but TUNE and even CW could make for a very hot box! Certainly ANY of these arrangements should never be attempted without a scope!! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Curt Nixon wrote: This is just my own experience running a T4x into a KW linear that needed 30W of drive (pair of 4cx300 grid driven) While the T4 loading control will reduce the output, it tends to make the output non-linear from the T4X. It is better, signal quality wise, to tune the load control properly and back off the power using the RF Gain control. In order to keep the gain control in a reasonable range, I used a 3dB attenuator in a small box in between the T4X and the Amp. This was a simple device made up of a TEE network of Ohmite non-inductive resistors. Use the formula for resistive attenuators for values. Very small, monolithic attenuators are now available from the likes of Anaren, and can be mounted on a small heatsink and work beautifully also. Sometimes available on auction for cheap. Still a good idea to use a monitor scope to be certain that everything is running in a linear manner. Loading and mismatch of T4x output and the Amp input can lead to much distortion and be non-apparent by viewing meters. FWIW Curt KU8L kc9...@aol.com wrote: Garey, Hi... I was just reading a post you made on reduced drive to the L-4B from the T-4any. You mentioned having the load at 0. Are you talking the T-4any or the L-4B as to the loading on 0...I suspect it is the T-4any. What if we load up the T-4any to a lower power out by putting the loading somewhere in between 0 and the max smoke position?? Are RF attenuators available somewhere? If this is the preferred way to do it? Who know...I might want to use my Alphs 91B with the T-4any? In that case I need 5-30 watts of drive. Thanks, Lee ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] L-4B reduced power
This is why I use a 100 watt dummy load, is has the capability to dissipate the heat of 75 watts. - Original Message - From: drakelist-boun...@zerobeat.net drakelist-boun...@zerobeat.net To: drakelist@zerobeat.net drakelist@zerobeat.net Sent: Tue Apr 26 10:59:55 2011 Subject: Re: [Drakelist] L-4B reduced power Curt - That is yet another way. I'm not sure why using reduced loading would make the output non-linear It's a 'linear' amplifier which implies that it's 'linear' from zero to full output. It may be that one of the lower level stages are distorting, but I'm not sure why they would. Using the Mic GAIN to reduce output is ok, but you begin to run into S/N problems in the AF and BAL MOD stages. Your three dB pad would certainly help in that regard. Of course you always have the 'possibility' that the MIC GAIN gets left too high from barefoot operation or other accident which would probably blow the grids, (but perhaps not.) Obviously the 3 dB pad has to dissipate whatever power is not fed through to the amplifier. Short duty cycle of SSB might help somewhat, but TUNE and even CW could make for a very hot box! Certainly ANY of these arrangements should never be attempted without a scope!! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Curt Nixon wrote: This is just my own experience running a T4x into a KW linear that needed 30W of drive (pair of 4cx300 grid driven) While the T4 loading control will reduce the output, it tends to make the output non-linear from the T4X. It is better, signal quality wise, to tune the load control properly and back off the power using the RF Gain control. In order to keep the gain control in a reasonable range, I used a 3dB attenuator in a small box in between the T4X and the Amp. This was a simple device made up of a TEE network of Ohmite non-inductive resistors. Use the formula for resistive attenuators for values. Very small, monolithic attenuators are now available from the likes of Anaren, and can be mounted on a small heatsink and work beautifully also. Sometimes available on auction for cheap. Still a good idea to use a monitor scope to be certain that everything is running in a linear manner. Loading and mismatch of T4x output and the Amp input can lead to much distortion and be non-apparent by viewing meters. FWIW Curt KU8L kc9...@aol.com wrote: Garey, Hi... I was just reading a post you made on reduced drive to the L-4B from the T-4any. You mentioned having the load at 0. Are you talking the T-4any or the L-4B as to the loading on 0...I suspect it is the T-4any. What if we load up the T-4any to a lower power out by putting the loading somewhere in between 0 and the max smoke position?? Are RF attenuators available somewhere? If this is the preferred way to do it? Who know...I might want to use my Alphs 91B with the T-4any? In that case I need 5-30 watts of drive. Thanks, Lee ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] L-4B reduced power
That's ok, but the transmitter is also loading into a 25 ohm load, or 2:1 SWR. Not that that is particularly bad, but it might limit the transmitter capability. Have you ever used a scope to see what the signal looks like? I know several people who have used this method, but none have ever really evaluated the signal quality. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com John Hudson wrote: This is why I use a 100 watt dummy load, is has the capability to dissipate the heat of 75 watts. - Original Message - From: drakelist-boun...@zerobeat.netdrakelist-boun...@zerobeat.net To: drakelist@zerobeat.netdrakelist@zerobeat.net Sent: Tue Apr 26 10:59:55 2011 Subject: Re: [Drakelist] L-4B reduced power Curt - That is yet another way. I'm not sure why using reduced loading would make the output non-linear It's a 'linear' amplifier which implies that it's 'linear' from zero to full output. It may be that one of the lower level stages are distorting, but I'm not sure why they would. Using the Mic GAIN to reduce output is ok, but you begin to run into S/N problems in the AF and BAL MOD stages. Your three dB pad would certainly help in that regard. Of course you always have the 'possibility' that the MIC GAIN gets left too high from barefoot operation or other accident which would probably blow the grids, (but perhaps not.) Obviously the 3 dB pad has to dissipate whatever power is not fed through to the amplifier. Short duty cycle of SSB might help somewhat, but TUNE and even CW could make for a very hot box! Certainly ANY of these arrangements should never be attempted without a scope!! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Curt Nixon wrote: This is just my own experience running a T4x into a KW linear that needed 30W of drive (pair of 4cx300 grid driven) While the T4 loading control will reduce the output, it tends to make the output non-linear from the T4X. It is better, signal quality wise, to tune the load control properly and back off the power using the RF Gain control. In order to keep the gain control in a reasonable range, I used a 3dB attenuator in a small box in between the T4X and the Amp. This was a simple device made up of a TEE network of Ohmite non-inductive resistors. Use the formula for resistive attenuators for values. Very small, monolithic attenuators are now available from the likes of Anaren, and can be mounted on a small heatsink and work beautifully also. Sometimes available on auction for cheap. Still a good idea to use a monitor scope to be certain that everything is running in a linear manner. Loading and mismatch of T4x output and the Amp input can lead to much distortion and be non-apparent by viewing meters. FWIW Curt KU8L kc9...@aol.com wrote: Garey, Hi... I was just reading a post you made on reduced drive to the L-4B from the T-4any. You mentioned having the load at 0. Are you talking the T-4any or the L-4B as to the loading on 0...I suspect it is the T-4any. What if we load up the T-4any to a lower power out by putting the loading somewhere in between 0 and the max smoke position?? Are RF attenuators available somewhere? If this is the preferred way to do it? Who know...I might want to use my Alphs 91B with the T-4any? In that case I need 5-30 watts of drive. Thanks, Lee ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] SW-4A amp
The SW-4A amp is not push pull, neither is the amp in the R-4A or R-4B. However, the SW-4 does have a push pull amp with two 6AQ5s and 1/2 of a 12AX7 as a phase inverter. Most audio amps consist of two stages. The first is a voltage amp, usually a triode such as one unit of a 12AX7 but sometimes pentodes are used such as the 6GX6 used in the R-4. The second audio stage is a power amp, usually either a power pentode such as the 6EH5 used in the R-4, R-4A and R-4B, or a beam pentode (6AQ5) as used in the SW-4. There are a wide variety of triodes and pentodes used in audio circuits. There is little point in using a push pull audio stage in a communications receiver due to the restricted audio frequencies used. A push pull audio stage requires two more tubes - a triode phase inverter and a second output tube - plus additional capacitors and resistors so it was not cost effective for most applications. John, VE3PMA ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] SW-4A amp
A transistorized PP stage can be of significant benefit in a Drake receiver. I was able to reduce the heat and current demands using a simple PP design in a R-4B. The added benefit is extremely low noise, low quiescent current, and low distortion without the need for an audio output transformer. However, one significant factor is that a stable, decoupled low-voltage line is necessary to power the PP circuit and is likely beyond the ability of most existing Drake LV supplies. But if the Drake LV supply is modified, it can offer tremendous increases in operating efficiency and performance over that of the single-stage VT design. Paul, W9AC - Original Message - From: John Boyle To: drakelist@zerobeat.net Sent: Tuesday, April 26, 2011 2:55 PM Subject: [Drakelist] SW-4A amp The SW-4A amp is not push pull, neither is the amp in the R-4A or R-4B. However, the SW-4 does have a push pull amp with two 6AQ5s and 1/2 of a 12AX7 as a phase inverter. Most audio amps consist of two stages. The first is a voltage amp, usually a triode such as one unit of a 12AX7 but sometimes pentodes are used such as the 6GX6 used in the R-4. The second audio stage is a power amp, usually either a power pentode such as the 6EH5 used in the R-4, R-4A and R-4B, or a beam pentode (6AQ5) as used in the SW-4. There are a wide variety of triodes and pentodes used in audio circuits. There is little point in using a push pull audio stage in a communications receiver due to the restricted audio frequencies used. A push pull audio stage requires two more tubes - a triode phase inverter and a second output tube - plus additional capacitors and resistors so it was not cost effective for most applications. John, VE3PMA -- ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] L-4B reduced power
I always attributed the non-linearity to mismatch issues. As soon as impedance mismatch is present, the output can become distorted. Also, when speaking of using a scope on the output, you can't just monitor the amplitude envelope, you need to be looking at the trapezoid. When the loading is off of the optimum (which happens to be the point of maximum output) the sides of the trap become curved. Sucked in if you will. Or bulging out. Getting down to 50 W using the RF gain control isn't too big an issue with S/N but going down to 10-30 is. Thus the 50 ohm attenuator. THe Anaren 100W monolithic units are about 3/4 x 1/2 and must be mounted on a faily substantial heat sink. I use one mounted to an old CPU finned unit with fan but never really need the fan for CW or SSB. I used one to run the TR7 down to below 1W for a QRP WAS contest in January. Hardly gets warm. THe one for the amp, with resistors, is in a box 4x4x3 and unless you run AM or extended RTTY, the resistors don't have to be capable of anywhere near the full difference in power. Bite the bullet and do it the proper way--use a 50 ohm attenuator. FWIW Curt KU8L Garey Barrell wrote: That's ok, but the transmitter is also loading into a 25 ohm load, or 2:1 SWR. Not that that is particularly bad, but it might limit the transmitter capability. Have you ever used a scope to see what the signal looks like? I know several people who have used this method, but none have ever really evaluated the signal quality. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com John Hudson wrote: This is why I use a 100 watt dummy load, is has the capability to dissipate the heat of 75 watts. - Original Message - From: drakelist-boun...@zerobeat.netdrakelist-boun...@zerobeat.net To: drakelist@zerobeat.netdrakelist@zerobeat.net Sent: Tue Apr 26 10:59:55 2011 Subject: Re: [Drakelist] L-4B reduced power Curt - That is yet another way. I'm not sure why using reduced loading would make the output non-linear It's a 'linear' amplifier which implies that it's 'linear' from zero to full output. It may be that one of the lower level stages are distorting, but I'm not sure why they would. Using the Mic GAIN to reduce output is ok, but you begin to run into S/N problems in the AF and BAL MOD stages. Your three dB pad would certainly help in that regard. Of course you always have the 'possibility' that the MIC GAIN gets left too high from barefoot operation or other accident which would probably blow the grids, (but perhaps not.) Obviously the 3 dB pad has to dissipate whatever power is not fed through to the amplifier. Short duty cycle of SSB might help somewhat, but TUNE and even CW could make for a very hot box! Certainly ANY of these arrangements should never be attempted without a scope!! 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs www.k4oah.com Curt Nixon wrote: This is just my own experience running a T4x into a KW linear that needed 30W of drive (pair of 4cx300 grid driven) While the T4 loading control will reduce the output, it tends to make the output non-linear from the T4X. It is better, signal quality wise, to tune the load control properly and back off the power using the RF Gain control. In order to keep the gain control in a reasonable range, I used a 3dB attenuator in a small box in between the T4X and the Amp. This was a simple device made up of a TEE network of Ohmite non-inductive resistors. Use the formula for resistive attenuators for values. Very small, monolithic attenuators are now available from the likes of Anaren, and can be mounted on a small heatsink and work beautifully also. Sometimes available on auction for cheap. Still a good idea to use a monitor scope to be certain that everything is running in a linear manner. Loading and mismatch of T4x output and the Amp input can lead to much distortion and be non-apparent by viewing meters. FWIW Curt KU8L kc9...@aol.com wrote: Garey, Hi... I was just reading a post you made on reduced drive to the L-4B from the T-4any. You mentioned having the load at 0. Are you talking the T-4any or the L-4B as to the loading on 0...I suspect it is the T-4any. What if we load up the T-4any to a lower power out by putting the loading somewhere in between 0 and the max smoke position?? Are RF attenuators available somewhere? If this is the preferred way to do it? Who know...I might want to use my Alphs 91B with the T-4any? In that case I need 5-30 watts of drive. Thanks, Lee ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
Re: [Drakelist] SW-4A amp
- Original Message - From: John Boyle jmbo...@ripnet.com To: drakelist@zerobeat.net Sent: Tuesday, April 26, 2011 11:55 AM Subject: [Drakelist] SW-4A amp The SW-4A amp is not push pull, neither is the amp in the R-4A or R-4B. However, the SW-4 does have a push pull amp with two 6AQ5s and 1/2 of a 12AX7 as a phase inverter. Most audio amps consist of two stages. The first is a voltage amp, usually a triode such as one unit of a 12AX7 but sometimes pentodes are used such as the 6GX6 used in the R-4. The second audio stage is a power amp, usually either a power pentode such as the 6EH5 used in the R-4, R-4A and R-4B, or a beam pentode (6AQ5) as used in the SW-4. There are a wide variety of triodes and pentodes used in audio circuits. There is little point in using a push pull audio stage in a communications receiver due to the restricted audio frequencies used. A push pull audio stage requires two more tubes - a triode phase inverter and a second output tube - plus additional capacitors and resistors so it was not cost effective for most applications. John, VE3PMA I think audio amplfier quality can have a significant effect in a communications receiver despite the narrow band of audio frequencies handled. This is because distortion, both harmonic and intermodulation, can exagerate the effect of noise. Single-ended amplifiers can be made to have reasonably low distortion by carful design and the use of some negative feedback. The advantages of push-pull are that even harmonics are automatically supressed and that core saturation from unbalanced DC in the transformer windings is eliminated. Core saturation reduceds low frequency responce but can also cause distortion. Intermodulation distortion is often overlooked but it can have a significant effect on narrow band information even including CW. For the most part push-pull amplifiers are not used in tube communications receivers because of the added complication, as you describe, plus the lack of necessity for either high audio power or amplifier efficiency. Feedback also is seldom found in single-ended amps because it requires more gain and a higher quality output transformer, both of which drive cost up. Its an interesting experiment to pick off the audio from the detector stage of a receiver and feed to a good quality amplfier driving the usual receiver loudspeaker. Sometimes the difference is quite amazing. -- Richard Knoppow Los Angeles WB6KBL dickb...@ix.netcom.com ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] Re TR-3 fixed
Hi Gang, Well, it's great news, I finally got my TR-3 working. Lots of tense moments, as I mentioned in my last post, the short circuit pointed straight to the meter itself. I still can't believe a meter could draw that much amperage. It made the carbon trace in the zeroing pot red hot. Luckily Carl has a parts TR-4 He sold me a meter but before I installed it, I used another idea gleaned from a fellow Drakelister's email. He said to solder a resistor in the meter circuit, and monitor the voltage across it. When I did that everything was OK. So I installed the new meter, now it reads correctly for signal strength, as well as cranking the RF gain down. Boy does that make me esthetic, not only that, but I'm happy. Tom, WD8JPP ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
[Drakelist] R4A filter location
Where physically in the R4A is the crystal lattice filter? ___ Drakelist mailing list Drakelist@zerobeat.net http://mailman.zerobeat.net/mailman/listinfo/drakelist
