Check out the specs at Duncan Amps TDSL.... TDSL Tube search
The tubes above won't be happy above 350V input and are rated for less current the the 5AR4, 5U4, 5R4, etc.
Most of the common octal rectifiers are the same pin-out, so there is no rewiring involved. Just replace the 5AR4 with the new tube.
A 5Y3(or 4) can't pass the current that your amp needs, and has a low voltage drop, a double-whammy in the case of your needs.
A 5Y3(or 4) can't pass the current that your amp needs, and has a low voltage drop, a double-whammy in the case of your needs.
quote:
I've dealt with instructions to measure voltages without the tubes, in Bottlehead and Dynaco amps. What you are doing is matching up the manufacturer's experience with yours. It is good to know that you have an unloaded voltage that is within range of what is spec'ed, even though it is NOT what you'll get with the tubes in. I'm sort of dumbfounded that nobody here recognized this.
Please guide me toward the unloaded voltages that one should get without tubes present. I am not finding them in the Dynaco Stereo 70 instructions or the SDS Labs (Triode Electronics) literature.
I have 454VDC at (C), and 442 at (B) in the power supply with tubes present and bias adjusted correctly. I have 454VDC off the rectifier tube. This is with a AC line voltage of 122 volts.
I have 521VDC at the rectifier with no other tubes installed. This is with a stock power supply.
I've dealt with instructions to measure voltages without the tubes, in Bottlehead and Dynaco amps. What you are doing is matching up the manufacturer's experience with yours. It is good to know that you have an unloaded voltage that is within range of what is spec'ed, even though it is NOT what you'll get with the tubes in. I'm sort of dumbfounded that nobody here recognized this.
Please guide me toward the unloaded voltages that one should get without tubes present. I am not finding them in the Dynaco Stereo 70 instructions or the SDS Labs (Triode Electronics) literature.
I have 454VDC at (C), and 442 at (B) in the power supply with tubes present and bias adjusted correctly. I have 454VDC off the rectifier tube. This is with a AC line voltage of 122 volts.
I have 521VDC at the rectifier with no other tubes installed. This is with a stock power supply.
That seems good.
Well... ST70's are notorious for eating rectifiers for lunch. The original design ran the tube right at the limits, and that was assuming a genuine Mullard-built GZ34/5AR4. That the modern ones can't take it is not much of a surprise.
The output tube failure and the cathode resistor failure are two sides of the same coin. One can lead to the other. Don't sweat it.
Um, I would suggest holding off from that... If you want to throw away some B+ voltage, just replace the 5AR4 with a 5R4 before adding a resistor to the circuit. The resistor will adversely effect the bias circuit and mainly just make things warmer. It also might add hum, as you are changing the ground potential of the B+ supply.
Here are my suggestions.
Get yourself a new set of Russian EL34s. I like SED winged "C", but the various brands sold by New Sensor (Sovtek, Svetlana, EH, Mullard, Tung-sol) are all good as well. The EH and Mullard will be the premium product, and most likely the most durable. Install and bias properly.
For the rectifier I think you have 2 good choices - Buy a new Sovtek 5AR4 and get a Pearl Tube Cooler. The cooler solved all my blown rectifier problems in my ST70. (Parts Conexion has them) or get an Octal-plug solid state replacement diode thingy from Triode Electronics. (it will have the proper voltage drop)
With all this new shiny stuff installed, take a set of voltage readings and write them down somewhere where you can find them again. In about 50-100hr of use on the new tubes, re-check and set the bias and take another set of voltages. (It's good to have notes on this stuff for when things break)
My suspicion is that you had a bit of bad luck, and all your failures happened at once. A new set of tubes is not cheap, but it might not be a bad idea to get a new, durable set and go from there.
Nothing to do with the Bias circuit and won't add hum because the filtering will be less hammered.
Here's a total explaination of the problem with fried 5AR4's from the Valve Wizard site:
Scroll down to the last line first and then come back up and get schooled.
Thank you Valve Wizard,
Minimum Limiting Resistance:
A valve rectifiers must have a resistance in series with each anode. Many 'classic' amps do not include these when they ought to, and rectifier failure is common in these amps. The data sheet will provide a Minimum Limiting Resistance (Rlim(min)) for different supply voltages, although the limiting resistance can be decreased if the reservoir capacitor is also decreased proportionately. Part of the limitng resistance will be made up of unavoidable transformer resistance and reflected impedance, and this should be calculated first in order to find out whether any additonal resistance must be added.
For example, when supplied by a transformer rated at 300-0-300Vrms, the EZ80 specifies Rlim(min) = 215 ohms per anode. The total impedance presented to the rectifier by the transformer is given by:
Rt= Rs + (n^2)* Rp
Where:
Rs = DC resistance of one half of the transformer secondary winding.)
Rp = DC resistance of the transformer primary winding.
n = Secondary to primary turns ratio (equal to the secondary voltage divided by the primary supply voltage).
If we were using a mains transformer with a 240V; 80R primary and a 310-0-310V; 50R per half secondary:
Rt= 50 + (1.29^2)* 80 = 183R
The EZ80 requires at least 215 ohms, so an additonal 215 - 183 = 32 ohm resistor must be placed in series with each anode (so we would probably use 33 or 47 ohms).
Because the limiting resistors will have to carry the ripple current of the reservoir capacitor it is best to use high wattage resistors. Even 7W resistors will usually get quite warm. Remember that the voltage drop across the limiting resistors will cause the HT fall proportionately.
Alternatively, a single limiting resistor could be placed between the transformer centre tap and ground, although its power dissipation will be doubled.
Another option and less expensive then the SS plug in is to use 1N4007 or better yet UF4007 SS diodes in series from PS trans leads to pins 4 and 6 of your 5AR4. UF5408 is larger and would work too. You then can keep your 5AR4 for the slow warmup benefit. Google Geek Zone or scorpiorising.ca to find Gregg or as "Geek" who also posts on this site. He as power supply mods for ST70 incuding replacing the Tube Rectifier on his site. He uses 75 ohm 10 W ceramic resistors in series with 4 diodes for his SS rectifier replacement in place of the 5AR4. For a total Tube Rect. replacement UF5408 might be better as higher Amperage rated. SS Diodes are 50 cents or less too.
Many of the big amps from Harman Kardon, Heathkit, Macintosh etc. did away with the tube rectfier as an improvement.
It has been said on a big amp like the ST70 tube rectifiers "add sog to the bass, blur the mids, and dull the highs. Tube "Tone" is a great sonic high, but can I have some detail to go along with it please?"
EH 6CA7 is said to be a nice tube if you don't want to spend a lot. Genelex Gold Lions for a fair bit more money are really liked. KT-66 is said to be really nice. Shuguang Treasure Series are well liked too.
Many of the big amps from Harman Kardon, Heathkit, Macintosh etc. did away with the tube rectfier as an improvement.
It has been said on a big amp like the ST70 tube rectifiers "add sog to the bass, blur the mids, and dull the highs. Tube "Tone" is a great sonic high, but can I have some detail to go along with it please?"
EH 6CA7 is said to be a nice tube if you don't want to spend a lot. Genelex Gold Lions for a fair bit more money are really liked. KT-66 is said to be really nice. Shuguang Treasure Series are well liked too.
Last edited:
I should have mentioned in my post that I moved the AC to pin 3 and pin 5 and installed a 1N4007 diode from pin 3 to pin 4 and from pin 5 to pin 6. This takes the work from the 5AR4 but still allows for the slow warm up feature.
quote:
It has been said on a big amp like the ST70 tube rectifiers "add sog to the bass, blur the mids, and dull the highs. Tube "Tone" is a great sonic high, but can I have some detail to go along with it please?"
Have seen no difference between tube rectifiers and SS rectifiers once the junk stock Dynaco driver board was replaced with something better. Just my .02😎
It has been said on a big amp like the ST70 tube rectifiers "add sog to the bass, blur the mids, and dull the highs. Tube "Tone" is a great sonic high, but can I have some detail to go along with it please?"
Have seen no difference between tube rectifiers and SS rectifiers once the junk stock Dynaco driver board was replaced with something better. Just my .02😎
Quote:
It just baffled me that i lost so many rectifiers, then a 10ohm cathode resistor and then a power tube. must have just been bad luck.
Sound to me like maybe the bias was cranked up too much on one or both of the output tubes.
I think we need to start at square one. Get some tubes in it, turn the bias down. Turn it on, check voltages and bias it up. Check voltages again and then make an evaluation after that. Worry about the damn voltage being too high after getting it running properly.
It just baffled me that i lost so many rectifiers, then a 10ohm cathode resistor and then a power tube. must have just been bad luck.
Sound to me like maybe the bias was cranked up too much on one or both of the output tubes.
I think we need to start at square one. Get some tubes in it, turn the bias down. Turn it on, check voltages and bias it up. Check voltages again and then make an evaluation after that. Worry about the damn voltage being too high after getting it running properly.
I have never seen anything referring to this in the time I have been into DIY audio.
I stand humbled and corrected.
6BG6GA said:
I agree wholeheartedly!
i ordered some shiny new stuff. one matched pair of SED winged C el34s and on matched pair of el34s by electro harmonics . i already have a SS rectifier installed along with the CL90 . i will make notes of the voltage readings.i also ordered a potato masher 5r4 for experimentation .
you say that the SS replacement from triode will have the proper voltage drop. does it have a resistor inside it? the copper cap rectifier does but i couldnt find any info on what is inside the tssr01 unit from triode.
when you say turn down the bias do you suggest then to adjust it to about -1.3 volts or so?
thanks for the advice
Quote:
when you say turn down the bias do you suggest then to adjust it to about -1.3 volts or so?
Turn the bias controls fully counterclockwise.
I would suggest no shinney new tubes in that muther until its up and running properly. Once it is then put in the new tubes and enjoy it.
I really suggest that you do NOT worry about the voltages right now that YOU consider to be incorrect and high. I posted my voltages at the power supply both unloaded and with tubes and biased up correctly. I am within 1 volt AC of what you are getting from the wall socket and that difference may or may not be a difference in the meters that we are using. I don't consider my voltages to be incorrect and or too high.
when you say turn down the bias do you suggest then to adjust it to about -1.3 volts or so?
Turn the bias controls fully counterclockwise.
I would suggest no shinney new tubes in that muther until its up and running properly. Once it is then put in the new tubes and enjoy it.
I really suggest that you do NOT worry about the voltages right now that YOU consider to be incorrect and high. I posted my voltages at the power supply both unloaded and with tubes and biased up correctly. I am within 1 volt AC of what you are getting from the wall socket and that difference may or may not be a difference in the meters that we are using. I don't consider my voltages to be incorrect and or too high.
Yes, the SS replacement rectifiers that are in an octal plug have a resistor to simulate the fwd voltage drop of a tube diode.
I suggest talking to the guys at triode (Carl?) about the best choice for your amp.
I mean to just properly set the bias as per the Triode electronics manual. Bias can/will shift with both a new rectifier and new output tubes. Don't do anything other than set the bias it where it is supposed to be. After some use, and the tubes settle in, check it again, and adjust if necessary.
How far away from optimal is the 'bad' set of tubes biasing? (What voltage should they read, and what are you getting?)
If you can bias one side, but not the other (Which I think is what you are saying),
Swap the set of output tubes from one side to the other. If the side you can (or can't) bias moves with the tubes, then that pair of tubes are the problem.
If you can bias one side, but not the other (Which I think is what you are saying),
Swap the set of output tubes from one side to the other. If the side you can (or can't) bias moves with the tubes, then that pair of tubes are the problem.
- Status
- Not open for further replies.