I have two Marantz Model Five amplifiers that I inherited from my Dad after he passed away. They've been sitting in an air conditioned upstairs room for probably 30 years; they're in pristine physical condition. They are all original except for two 0.1u caps that he added to create a center tap on the primary of the power transformer. I'd like to recap them and put them in service again. I'm thinking that as long as I'm at it, I should also replace the carbon composition resistors as well.
Other than the usual cautions about working on tube gear, does anyone have any thoughts or advice before I start?
Thanks.
Everett
Other than the usual cautions about working on tube gear, does anyone have any thoughts or advice before I start?
Thanks.
Everett
Before you do anything . . .
Inspect every thing. Look for corrosion, bad aged solder joints, etc.
Use a Variac or Bulb limiter to bring the amplifier up slowly.
Verify if it works.
If it does not work, troubleshoot and fix.
Only then, should you wholesale replace any components.
Inspect every thing. Look for corrosion, bad aged solder joints, etc.
Use a Variac or Bulb limiter to bring the amplifier up slowly.
Verify if it works.
If it does not work, troubleshoot and fix.
Only then, should you wholesale replace any components.
Seconded, do not replace any parts unless clearly necessary due to failure.
Except for the added death caps, which I would immediately remove by cutting their leads at their solder joints.
But do use a Variac to soft start it and reform the capacitors. Bulb limiters do not do this.
Carbon resistors can work fine after a long time in storage, if kept away from moisture.
Then there's the value to a collector, which would be much less for a hacked on unit.
Except for the added death caps, which I would immediately remove by cutting their leads at their solder joints.
But do use a Variac to soft start it and reform the capacitors. Bulb limiters do not do this.
Carbon resistors can work fine after a long time in storage, if kept away from moisture.
Then there's the value to a collector, which would be much less for a hacked on unit.
.... "Then there's the value to a collector, which would be much less for a hacked on unit."
This was/is one of my main concerns.
Have the variac. In fact, it's reforming the caps in an old piece of solid state SAE equipment as I type this.
Have the dim bulb limiter as well.
Thanks.
Everett
This was/is one of my main concerns.
Have the variac. In fact, it's reforming the caps in an old piece of solid state SAE equipment as I type this.
Have the dim bulb limiter as well.
Thanks.
Everett
The bulb limiter cannot be used while performance testing the amplifier, or during biasing.
Just upon initial power up in case of a catastrophic failure, and maybe during a burn-in.
Make certain your Variac output is the correct rated AC input voltage to the amplifier.
Some Variacs are wired differently from the dial markings, and can be way off.
Just upon initial power up in case of a catastrophic failure, and maybe during a burn-in.
Make certain your Variac output is the correct rated AC input voltage to the amplifier.
Some Variacs are wired differently from the dial markings, and can be way off.
When you do take the plunge and start it up for the first time, I think it is useful to be ready to measure all voltages on tube pins, whilst keeping an eye out for red plates or other signs all is not well. Then you can turn off and assess the voltages and look for outliers or obvious variance. If you post the results here I am sure some of the guys here could see if there is a voltage that is suspect.
If it hums when it warms up, I have discovered that sometimes just not being in use for a long time can be a factor, due to the old electrolytics, so if the voltages check out you can be patient with it and maybe it solves itself.
If it hums when it warms up, I have discovered that sometimes just not being in use for a long time can be a factor, due to the old electrolytics, so if the voltages check out you can be patient with it and maybe it solves itself.
Thanks everyone. I'll put it on a Variac along with the dim bulb limiter and bring it up very slowly with a resistor on the output while looking for any issues.
Be careful with variac and tube amplifiers because you could burn the output tubes by having too low bias voltage.
Regards,
Regards,
blek stena,
If the output tubes use Self Bias, there will always be enough bias voltage when you bring up the line voltage with a variac.
One more reason to use self bias!
Yes, I admit, other bias methods have their advantages too, versus self bias.
I have used Fixed Adjustable Bias, Battery Bias, and Self Bias . . .
All have tradeoffs.
If the output tubes use Self Bias, there will always be enough bias voltage when you bring up the line voltage with a variac.
One more reason to use self bias!
Yes, I admit, other bias methods have their advantages too, versus self bias.
I have used Fixed Adjustable Bias, Battery Bias, and Self Bias . . .
All have tradeoffs.
I don't believe any of the original Marantz tube amplifiers used self bias.
The two 0.1 uF caps connected to the power line are a safety hazard and should be removed. If it's connected to an ungrounded outlet and you come between its chassis and ground, you could conduct as much as 5 mA - not fatal but could cause you to flinch or drop something. That's assuming that the capacitors are good... it could be worse.
rayma,
No schematic posted.
If any of you searched the web for a schematic, and you found one, then by all means, post it in this thread, please.
Mr. Marantz has almost certainly passed away; Sony bought the Marantz rights; are the amplifier schematics still copyrighted?
No matter what company uses Fixed, Fixed Adjustable, Battery, Gardner Cross bias, or Self bias, the unique advantages and disadvantages of each Bias circuit are according to the circuit topology.
I was putting in a Plug for Self Bias.
Use it or suffer the consequences, if any.
I remember the engineer who always changed Dyna Stereo 70 amplifiers from a very poor example of fixed adjustable bias,
to self bias.
Lost a little output power.
Gained reliability, the Ability to use tubes that are Not Perfectly matched, etc.
No schematic posted.
If any of you searched the web for a schematic, and you found one, then by all means, post it in this thread, please.
Mr. Marantz has almost certainly passed away; Sony bought the Marantz rights; are the amplifier schematics still copyrighted?
No matter what company uses Fixed, Fixed Adjustable, Battery, Gardner Cross bias, or Self bias, the unique advantages and disadvantages of each Bias circuit are according to the circuit topology.
I was putting in a Plug for Self Bias.
Use it or suffer the consequences, if any.
I remember the engineer who always changed Dyna Stereo 70 amplifiers from a very poor example of fixed adjustable bias,
to self bias.
Lost a little output power.
Gained reliability, the Ability to use tubes that are Not Perfectly matched, etc.
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rayma,
Thanks for posting the schematic.
Adjusting the output tube bias is a nightmare for anybody who does not know what they are doing.
Power cord removed, Check B+ for Remaining Lurking voltage.
Short the output transformer secondaries (a lot of DMMs will auto-range when measuring primary DCRs, the inductance causes that auto-range to hunt)
Measure the DCR from Plate one to the center tap, write it down.
Do the same for Plate two.
Remove secondary shorts
Get the amplifier up an running.
Caution, this measurement requires probes on high voltages.
Measure the difference of plate one voltage to the center tap voltage. That voltage, divided by primary 1/2 one DCR = plate current
Set tube one bias for correct current (calculate before hand, required current x DCR = voltage you need from plate to center tap.
Repeat for tube two, and primary 1/2 two.
Now, go back and re-adjust tube one bias, the current has changed when you set the bias on tube two.
go back to tube two, and re-adjust the bias (re-setting tube one affects tube tow current).
Are you tired yet?
So . . . do this instead:
You have a DMM that can measure low DC volts.
Then split the common cathode resistor of the push pull pair.
if you are worried about degeneration from the cathode resistors that are now separate, just use lower Ohm resistors.
No high voltage here.
Dyna Stereo 70 was even worse, only one bias pot per push pull pair.
Have you priced Quality Very Well Matched tubes lately?
Fix your bias sense resistor situation.
Low volts accurate DMMs are a dime a dozen. So are precision sense resistors.
We are no longer playing Repair Technician of the mid 50s and mid 60s.
Thanks for posting the schematic.
Adjusting the output tube bias is a nightmare for anybody who does not know what they are doing.
Power cord removed, Check B+ for Remaining Lurking voltage.
Short the output transformer secondaries (a lot of DMMs will auto-range when measuring primary DCRs, the inductance causes that auto-range to hunt)
Measure the DCR from Plate one to the center tap, write it down.
Do the same for Plate two.
Remove secondary shorts
Get the amplifier up an running.
Caution, this measurement requires probes on high voltages.
Measure the difference of plate one voltage to the center tap voltage. That voltage, divided by primary 1/2 one DCR = plate current
Set tube one bias for correct current (calculate before hand, required current x DCR = voltage you need from plate to center tap.
Repeat for tube two, and primary 1/2 two.
Now, go back and re-adjust tube one bias, the current has changed when you set the bias on tube two.
go back to tube two, and re-adjust the bias (re-setting tube one affects tube tow current).
Are you tired yet?
So . . . do this instead:
You have a DMM that can measure low DC volts.
Then split the common cathode resistor of the push pull pair.
if you are worried about degeneration from the cathode resistors that are now separate, just use lower Ohm resistors.
No high voltage here.
Dyna Stereo 70 was even worse, only one bias pot per push pull pair.
Have you priced Quality Very Well Matched tubes lately?
Fix your bias sense resistor situation.
Low volts accurate DMMs are a dime a dozen. So are precision sense resistors.
We are no longer playing Repair Technician of the mid 50s and mid 60s.
When Dynaco was producing the Stereo 70, they supplied matched pairs of Mullard output tubes.
A Mullard rectifier too. Their PAS preamp came with four Telefunken ECC83 tubes. Not bad, huh?
A Mullard rectifier too. Their PAS preamp came with four Telefunken ECC83 tubes. Not bad, huh?
rayma,
My worst and potentially most damaging Dyna Stereo 70 problem:
Each push pull pair of cathodes has a 1.56 Ohm common resistor to ground. A Cheap VOM measures a new carbon zinc battery, 1.56Volts.
Mark the needle position with a grease pen on the VOM's plastic front. Genius! substitutive accurate measurement!
Then the VOM measures across the 1.56 Ohm resistor, and the bias pot is adjusted for 1.56V on the VOM, 100mA for the EL34 pair.
Really accurate and a nice idea.
Well,
What happened was one of the "Black Beauty" coupling caps was Ugly-Leaky (The outside looked beautiful, but inside was a Tasmanian Devil).
One EL34 had 40mA of current, the other EL34 had 60mA of current.
Ouch!
The best laid plans of mice and men
I get Very Well Matched, and Very Well re-tested New JJ tubes at Eurotubes.com. I just drive right over and pick up a pair.
They have lots of test equipment, designed and built in house; and additional test equipment designed and built by another person who I worked with in the spectrum analyzer engineering group at Tektronix.
I also met Lynn Olson because he worked there too.
I am so fortunate and so blessed, both from Tektronix, and from many other employers too.
My worst and potentially most damaging Dyna Stereo 70 problem:
Each push pull pair of cathodes has a 1.56 Ohm common resistor to ground. A Cheap VOM measures a new carbon zinc battery, 1.56Volts.
Mark the needle position with a grease pen on the VOM's plastic front. Genius! substitutive accurate measurement!
Then the VOM measures across the 1.56 Ohm resistor, and the bias pot is adjusted for 1.56V on the VOM, 100mA for the EL34 pair.
Really accurate and a nice idea.
Well,
What happened was one of the "Black Beauty" coupling caps was Ugly-Leaky (The outside looked beautiful, but inside was a Tasmanian Devil).
One EL34 had 40mA of current, the other EL34 had 60mA of current.
Ouch!
The best laid plans of mice and men
I get Very Well Matched, and Very Well re-tested New JJ tubes at Eurotubes.com. I just drive right over and pick up a pair.
They have lots of test equipment, designed and built in house; and additional test equipment designed and built by another person who I worked with in the spectrum analyzer engineering group at Tektronix.
I also met Lynn Olson because he worked there too.
I am so fortunate and so blessed, both from Tektronix, and from many other employers too.
Unfortunately, a lot of those old Black Cat capacitors leaked enough to foul up the bias, for sure.
They just didn't know about it until a lot were in the field. Cost was not the issue.
They just didn't know about it until a lot were in the field. Cost was not the issue.
The old first in first out rule often applies to stocking parts, etc.
However, if a vendor changes their food, electronic part, chemical, etc. in any way, you may find you are out of any of those items that are useful to you anymore.
It caused problems at more than one technology company.
A few Decades ago,
I built a battery tester for batteries used in Ultrasound Dopplers used by Anesthetists, Surgeons, Obstetricians, etc.
Test open voltage, loaded voltage, and dynamic impedance including rise time and fall time.
We tested many companies batteries.
There was a definite conclusion, so we settled on one companies products.
Decades later, lots of that company's new batteries leak chemicals quite early in the use cycle, and even when not used, but slightly aged, way before the date code.
I have switched to another company's.
i hope the first company we picked solves their problem.
However, if a vendor changes their food, electronic part, chemical, etc. in any way, you may find you are out of any of those items that are useful to you anymore.
It caused problems at more than one technology company.
A few Decades ago,
I built a battery tester for batteries used in Ultrasound Dopplers used by Anesthetists, Surgeons, Obstetricians, etc.
Test open voltage, loaded voltage, and dynamic impedance including rise time and fall time.
We tested many companies batteries.
There was a definite conclusion, so we settled on one companies products.
Decades later, lots of that company's new batteries leak chemicals quite early in the use cycle, and even when not used, but slightly aged, way before the date code.
I have switched to another company's.
i hope the first company we picked solves their problem.
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Each push pull pair of cathodes has a 1.56 Ohm common resistor to ground. WRONG THEY ARE 15.6 Ohms A Cheap VOM measures a new carbon zinc battery, 1.56Volts.
Mark the needle position with a grease pen on the VOM's plastic front. Genius! substitutive accurate measurement!
Then the VOM measures across the 1.56 Ohm resistor, and the bias pot is adjusted for 1.56V on the VOM, 100mA for the EL34 pair. WRONG THEY ARE 15.6 Ohm, see how long your EL34s last with 100mA of current on a 450 volt supply.
Really accurate and a nice idea. WRONG again.
Does anyone expect an amplifier which is over 50 years old to have good electrolytic capacitors. Keep them at your own peril as they do make a really nice mess when they explode and leak their innards!
Want to reform them. Remove all tubes, keep a meter on capacitor C16 part 1 the 60mfd section. Increase the variac until this capacitor reaches 456 volts. Leave running for a couple of weeks.
We work on McIntosh and Marantz tube and solid state amplifiers. I always 100% replace all electrolytic capacitors if the client simply wants the amplifier "refreshed"
Mark the needle position with a grease pen on the VOM's plastic front. Genius! substitutive accurate measurement!
Then the VOM measures across the 1.56 Ohm resistor, and the bias pot is adjusted for 1.56V on the VOM, 100mA for the EL34 pair. WRONG THEY ARE 15.6 Ohm, see how long your EL34s last with 100mA of current on a 450 volt supply.
Really accurate and a nice idea. WRONG again.
Does anyone expect an amplifier which is over 50 years old to have good electrolytic capacitors. Keep them at your own peril as they do make a really nice mess when they explode and leak their innards!
Want to reform them. Remove all tubes, keep a meter on capacitor C16 part 1 the 60mfd section. Increase the variac until this capacitor reaches 456 volts. Leave running for a couple of weeks.
We work on McIntosh and Marantz tube and solid state amplifiers. I always 100% replace all electrolytic capacitors if the client simply wants the amplifier "refreshed"
MOER,
You are correct, 15.6 Ohms.
Not the 1.56 Ohms I stated, my mistake.
Who has ever replaced the 1.56 Ohm resistor in their Dyna stereo 70?
You would probably burn out the output transformer, EL34 tubes, rectifier, or B+ power supply, But only if the fuse in the primary did not blow open first . . . so that resistor never needs replacing if you want to keep the Dyna stock circuit.
Keep that 1.56 Ohm common cathode resistor in your Dyna if you want to, and know the total current for the push pull pair of tubes;
but never know if the two cathode currents are the same.
You would have to do separate measurements of each 1/2 of the primary DCRs, and the voltage drops in those DCRs to know the individual currents. That will only give you the screen current in 40% of the windings, plus the plate current in 100% of the windings.
Instead . . .
Do your customer a favor, add 2 test points, and change the two 15.6 Ohm resistors, into Four 31.2 Ohm resistors, one for each EL34.
Actually . . . with todays DMMs, and todays resistors, use 4 precision 10 Ohm resistors.
Then paste a paper on the inside of the bottom cover that documents the resistor change, and the location of the 4 test points.
I did not say 100mA for a single tube.
I said: "100mA for the EL34 pair". That is 50mA per tube, 100mA per push pull pair.
With each cathode current at 50mA, and the B+ at 450V (450V before the DCR voltage drop in the output transformer primary), then . . .
Worst Case: 50mA x 450V = 22.5 Watts total Plate Plus Screen dissipation.
Any good quality EL34 can run for a very, very long time if the plate dissipation Plus screen dissipation only totals 22.5 Watts.
The EL34 specifies max plate dissipation 25 Watts; and max screen dissipation 8 Watts = 33 Watts total.
I personally would never run an EL34 that hot.
Compare The Dyna's 22.5 Watts total dissipation, versus the data sheet's 33 Watts total dissipation for a single tube.
Then consider Bigs of California who ran their push pull amplifier a lot hotter than 22.5 Watts total plate plus screen dissipation.
Of course when it comes to the total heat in the glass envelope, do not forget the 6.3V x 1.5 Amps = another 9.45 Watts.
The above is First of all, a listing of my incorrect statement of the resistance value of the sense resistor,
The rest of my ramblings is some other information that might help some people to understand about dissipation, measurement, etd.
I am sorry that I upset you so badly.
If I had a customer who owned certain year models of Volkswagen bugs, I would recommend that I could add an Oil cooler radiator so that his
# 3 cylinder and piston would never sieze up.
Then I would leave the decision up to him.
You are correct, 15.6 Ohms.
Not the 1.56 Ohms I stated, my mistake.
Who has ever replaced the 1.56 Ohm resistor in their Dyna stereo 70?
You would probably burn out the output transformer, EL34 tubes, rectifier, or B+ power supply, But only if the fuse in the primary did not blow open first . . . so that resistor never needs replacing if you want to keep the Dyna stock circuit.
Keep that 1.56 Ohm common cathode resistor in your Dyna if you want to, and know the total current for the push pull pair of tubes;
but never know if the two cathode currents are the same.
You would have to do separate measurements of each 1/2 of the primary DCRs, and the voltage drops in those DCRs to know the individual currents. That will only give you the screen current in 40% of the windings, plus the plate current in 100% of the windings.
Instead . . .
Do your customer a favor, add 2 test points, and change the two 15.6 Ohm resistors, into Four 31.2 Ohm resistors, one for each EL34.
Actually . . . with todays DMMs, and todays resistors, use 4 precision 10 Ohm resistors.
Then paste a paper on the inside of the bottom cover that documents the resistor change, and the location of the 4 test points.
I did not say 100mA for a single tube.
I said: "100mA for the EL34 pair". That is 50mA per tube, 100mA per push pull pair.
With each cathode current at 50mA, and the B+ at 450V (450V before the DCR voltage drop in the output transformer primary), then . . .
Worst Case: 50mA x 450V = 22.5 Watts total Plate Plus Screen dissipation.
Any good quality EL34 can run for a very, very long time if the plate dissipation Plus screen dissipation only totals 22.5 Watts.
The EL34 specifies max plate dissipation 25 Watts; and max screen dissipation 8 Watts = 33 Watts total.
I personally would never run an EL34 that hot.
Compare The Dyna's 22.5 Watts total dissipation, versus the data sheet's 33 Watts total dissipation for a single tube.
Then consider Bigs of California who ran their push pull amplifier a lot hotter than 22.5 Watts total plate plus screen dissipation.
Of course when it comes to the total heat in the glass envelope, do not forget the 6.3V x 1.5 Amps = another 9.45 Watts.
The above is First of all, a listing of my incorrect statement of the resistance value of the sense resistor,
The rest of my ramblings is some other information that might help some people to understand about dissipation, measurement, etd.
I am sorry that I upset you so badly.
If I had a customer who owned certain year models of Volkswagen bugs, I would recommend that I could add an Oil cooler radiator so that his
# 3 cylinder and piston would never sieze up.
Then I would leave the decision up to him.
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