Hi Chris. You are right with the composite resistors. This was the reason for intending to replace them all. I already had ordered the necessary bigger resistors as MOX types. But the amp seems to work well and I will decide for further work after listening some time with my stereo system.
And wow, you have a great collection of very fine measurment instruments. Mine is not so big. Oscilloscopes, there I have many analog ones but only up to 100 MHz which are of course HP, old Textronix Series 7 and the German Hameg which now is merged into Rohde&Schwarz. And I have two digital scopes which are an old Gould and an Agilent. For quick setup measurement I prefer the analog ones since every knob has a dedicated function and I have not to dive into submenues like at the Agilent. If I need to store displays then the Agilent is of course better to use since I can transfer the curves to my PC and store it there.
My work on radio frequencies is limited. Just repairing FM stereo tuners, CB gear and airband RX. For this I use a generator from LEADER which provides a stereo MPX signal too. Unfortunately my 3455A multimeter has a defective voltage reference and I need to repair it. Other better multimeters I have Datron.
But in general I do not need this accuracy since working mainly on audio equipment the normal ones are sufficient. And when working on vacuum tube amps the tolerances of the circuit and the components are anyway very high.
Seasons Greetings, Sven
And wow, you have a great collection of very fine measurment instruments. Mine is not so big. Oscilloscopes, there I have many analog ones but only up to 100 MHz which are of course HP, old Textronix Series 7 and the German Hameg which now is merged into Rohde&Schwarz. And I have two digital scopes which are an old Gould and an Agilent. For quick setup measurement I prefer the analog ones since every knob has a dedicated function and I have not to dive into submenues like at the Agilent. If I need to store displays then the Agilent is of course better to use since I can transfer the curves to my PC and store it there.
My work on radio frequencies is limited. Just repairing FM stereo tuners, CB gear and airband RX. For this I use a generator from LEADER which provides a stereo MPX signal too. Unfortunately my 3455A multimeter has a defective voltage reference and I need to repair it. Other better multimeters I have Datron.
But in general I do not need this accuracy since working mainly on audio equipment the normal ones are sufficient. And when working on vacuum tube amps the tolerances of the circuit and the components are anyway very high.
Seasons Greetings, Sven
Hi Sven,
Agree on the accuracy for normal work. The problem is that cheap meters do not hold their calibration (many out out of tolerance right out of the box). That's why I use really good meters, and the darned things are still in tolerance after 25+ years! Analogue scopes are about the vest for our work. You have to buy silly expensive DSOs to even come close to an analogue scope. A DSO/MSO does have other valuable features (if you use them). Mine can capture a waveform and replay it out the arb generator output. That's pretty cool.
You don't need anywhere near what I have. I do a lot of other work and some research, so it demands the equipment I have. I just got an E36312A and EDU36311A pair of power supplies from Keysight. Great supplies, but the E36312A responds very slowly to keypad or web control inputs. Even a power supply can be important. The output noise is very low on these for example, and they read output voltage and current accurately. They even trend the outputs vs time. Very cool.
Now, Metal Oxide resistors are not that stable. If it is important, use a Metal Film. Metal Oxide are okay for dropping voltage where resistance change won't be an issue, but never in a feedback network for the regulator or an audio amplifier.
-Chris
Agree on the accuracy for normal work. The problem is that cheap meters do not hold their calibration (many out out of tolerance right out of the box). That's why I use really good meters, and the darned things are still in tolerance after 25+ years! Analogue scopes are about the vest for our work. You have to buy silly expensive DSOs to even come close to an analogue scope. A DSO/MSO does have other valuable features (if you use them). Mine can capture a waveform and replay it out the arb generator output. That's pretty cool.
You don't need anywhere near what I have. I do a lot of other work and some research, so it demands the equipment I have. I just got an E36312A and EDU36311A pair of power supplies from Keysight. Great supplies, but the E36312A responds very slowly to keypad or web control inputs. Even a power supply can be important. The output noise is very low on these for example, and they read output voltage and current accurately. They even trend the outputs vs time. Very cool.
Now, Metal Oxide resistors are not that stable. If it is important, use a Metal Film. Metal Oxide are okay for dropping voltage where resistance change won't be an issue, but never in a feedback network for the regulator or an audio amplifier.
-Chris
Hi Chris,
I agree to the MOX resistors. I put these into where slight resistance changes do not matter. With less digits multimeter I did not mean a simple handheld but a 4.5 digit hp or Keithley instead of a 6.5 one. I like the older meters with red LEDs instead of LCD which is often bad to read in distance at work. There I have a nice Philips which is 4.5 digits with setting possibility for 5.5 digits.
Sven
Hi Sven,
Yes, those are much better instruments. I also find LED displays easier to read. The new OLED ones are great, but they have a limited life and I'm very unhappy about that choice!
The main thing is that the meters you're using have actual input divider networks using close tolerance parts that are stable over time. The better instruments use a divider network on a ceramic substrate. This has a number of advantages including low inductance (better HF response) and thermal tracking. Never mind they are sealed and leakage currents are kept to a minimum depending on the PCB they are installed in. The 5 1/2 digit meters are great as well. One thing many don't pay attention to is the lowest range for DCV. You should be able to measure one digit beyond what you consider significant. That means a 100 mV scale with a 3 1/2 digit meter is completely useless, even more so when you look at the accuracy spec!
The amazing thing about the 34465A is the 100mV scale, with 4 digits to the right of the decimal! The current ranges are 1uA!!, AC response to 300 KHz which is common for the better meters these days. I just saw the current list price - yikes!
Interestingly, the old 3457A is 6 1/2 digit meter, but actually 7 1/2 digit via the GPIB buss. These are LCD display meters but would really improve your capabilities.
Yes, those are much better instruments. I also find LED displays easier to read. The new OLED ones are great, but they have a limited life and I'm very unhappy about that choice!
The main thing is that the meters you're using have actual input divider networks using close tolerance parts that are stable over time. The better instruments use a divider network on a ceramic substrate. This has a number of advantages including low inductance (better HF response) and thermal tracking. Never mind they are sealed and leakage currents are kept to a minimum depending on the PCB they are installed in. The 5 1/2 digit meters are great as well. One thing many don't pay attention to is the lowest range for DCV. You should be able to measure one digit beyond what you consider significant. That means a 100 mV scale with a 3 1/2 digit meter is completely useless, even more so when you look at the accuracy spec!
The amazing thing about the 34465A is the 100mV scale, with 4 digits to the right of the decimal! The current ranges are 1uA!!, AC response to 300 KHz which is common for the better meters these days. I just saw the current list price - yikes!
Interestingly, the old 3457A is 6 1/2 digit meter, but actually 7 1/2 digit via the GPIB buss. These are LCD display meters but would really improve your capabilities.
Hi Chris,
thanks for the tips. Since my work is just for myself I can choose according to the accuracy needed. For some audio measurements I still use special analog AC meters. These are from the 1970ies or so and never built again. All these I got used on the Bay. One measures audio frequencies down to 30µV full scale and has several filter curves built in. For audio FFT I use a USB sound box and several audio meas software. Unfortunately an professional Audio Precision analyzer is out my financial reach for this purpose.
Hi Sven,
I bought an RTX 6001 when the group buy was on. Fantastic instrument! Would I like an Audio Precision, or Keysight U8903B? Absolutely, but the RTX is right up there. Using M.I. it is fantastic, for quick jobs I have a paid copy of Arta.
I use some older 1970's AC voltmeters as well, can't beat the frequency response (10 MHz for the HP3400A) and I use an HP428A DC clamp on ammeter. Now that is a really cool instrument! Check those out, they can save you so much time! This was made up into the 1980's and uses vacuum tubes!
I bought an RTX 6001 when the group buy was on. Fantastic instrument! Would I like an Audio Precision, or Keysight U8903B? Absolutely, but the RTX is right up there. Using M.I. it is fantastic, for quick jobs I have a paid copy of Arta.
I use some older 1970's AC voltmeters as well, can't beat the frequency response (10 MHz for the HP3400A) and I use an HP428A DC clamp on ammeter. Now that is a really cool instrument! Check those out, they can save you so much time! This was made up into the 1980's and uses vacuum tubes!
Hi Chris,
OK, the RTX and Virtins is a very good solution, congratulate. But for me the need for extended measurements is seldom. So I live with ARTA (licenced) and a German program named audioTester which is easy to use. With the E-MU Tracker box I can measure up to almost 100 kHz. With a Bruel&Kjaer microphone I can view to ultrasound like from old remote controls and of course sound from bats. All this just for fun. Need seriously measure my stereo loudspeakers in my room in some time. The hp 3400A I have too. Interesting TRMS function with a thermal converter instead of an AD IC which are in later hp multimeters. DC clamps are hard to get and when they are very expensive at least here in Germany. Also the Tektronics clamps hard to get and often function is not warranted.
Your solution is pretty good too.
The DC clamp is massively helpful. The probe must come with the meter as they are calibrated together. If you see one at a decent price I recommend you grab it! I have two (one for each channel). These are extremely sensitive as well, better thna most clamps. They use a flux gate and balance circuit.
Yes, thermocouples are very common with RF power meters as well (have those too), but the newer ones are using chip solutions.
The DC clamp is massively helpful. The probe must come with the meter as they are calibrated together. If you see one at a decent price I recommend you grab it! I have two (one for each channel). These are extremely sensitive as well, better thna most clamps. They use a flux gate and balance circuit.
Yes, thermocouples are very common with RF power meters as well (have those too), but the newer ones are using chip solutions.
Hi Chris, for me it now late in the evening I will log out now. Hope to hear from you sometime later. By the way, if I did not mentioned yet, the DC300A works fine in my stereo system. Strong bass without additonal booming or lack of presence. For my old ears the highs are not so mandatory thus the possible distortion products from the midrange will not be heard really.
Hi Chris,
yes I think too. I like the bulky heavy power amplifiers. Perhaps newer designs of today products might be a little better but for my old ears (end is about 11 kHz depending on audio volume) it were overkill. My friends like and use tube amplifiers which sound also pretty good. But for my music with strong bass content and thirsty loudspeakers I would need very big and expensive tube amplifiers where I don't like to spend the money for. For guitar I use of course tube amps only. But this is not hi-fi but sound creation. Part of money goes to the hobby of my son and me. This is vintage Chevrolet and Ford cars.
Hi radiogaga,
You know, old ears can hear just fine. Also, if it sounds like the real, live thing ... that is high fidelity no matter what your hearing curve is like. People miss that.
Yeah, a CJ Premier One was one to think twice about. Reliable, but 6 x KT88 per channel. 250 watts per channel the hard way! Anything similar would be in the same boat. I don't mind a 20 to 80 watt aside amp using one pair of output tubes as long as the design was reliable. Lot's of pure junk out these days. Still I commonly run to my solid state amplifier as I like to turn it up. Mine are 86 to 87 dB/watt efficient, 4 ohm. Not great. I would love a pair of Klipsch 7 III, maybe some day.
Old designs are often updated and improved for very high performance. I wouldn't say new power amps, except a very few, are truly better to be honest. They are more cheaply manufactured and tend to fail sooner as headroom in the design is not used now. Headroom meaning voltage and power. Current too of course. The average amplifier made around 1980, plus or minus a few years, are probably the best. There are some (Marantz 500) earlier and later in design that are exemplary, but the bulk of really good sounding, reliable products were made then. By 1990 I wasn't interested in seeing new product service manuals except to see what I was going to have to deal with. Exemptions would be Cyrus and McIntosh (they were improving year by year) and later Marantz once Philips was no longer involved. Denon and a few others made some really good stuff, but not constructed solidly anymore.
I service guitar amps as well. Yes, tube is the only way to go. Having said that, a Yamaha with proper effects unit was excellent too. The proper effects unit being the one that had the sound you wanted.
-Chris
You know, old ears can hear just fine. Also, if it sounds like the real, live thing ... that is high fidelity no matter what your hearing curve is like. People miss that.
Yeah, a CJ Premier One was one to think twice about. Reliable, but 6 x KT88 per channel. 250 watts per channel the hard way! Anything similar would be in the same boat. I don't mind a 20 to 80 watt aside amp using one pair of output tubes as long as the design was reliable. Lot's of pure junk out these days. Still I commonly run to my solid state amplifier as I like to turn it up. Mine are 86 to 87 dB/watt efficient, 4 ohm. Not great. I would love a pair of Klipsch 7 III, maybe some day.
Old designs are often updated and improved for very high performance. I wouldn't say new power amps, except a very few, are truly better to be honest. They are more cheaply manufactured and tend to fail sooner as headroom in the design is not used now. Headroom meaning voltage and power. Current too of course. The average amplifier made around 1980, plus or minus a few years, are probably the best. There are some (Marantz 500) earlier and later in design that are exemplary, but the bulk of really good sounding, reliable products were made then. By 1990 I wasn't interested in seeing new product service manuals except to see what I was going to have to deal with. Exemptions would be Cyrus and McIntosh (they were improving year by year) and later Marantz once Philips was no longer involved. Denon and a few others made some really good stuff, but not constructed solidly anymore.
I service guitar amps as well. Yes, tube is the only way to go. Having said that, a Yamaha with proper effects unit was excellent too. The proper effects unit being the one that had the sound you wanted.
-Chris
Hi Chris,
well spoken. For the young people sound modeling is the future. Also since the art of music changed. Much electronic stuff. Also real good music. But I am old school, so I leave it to them. I still stick with performers approx. to the 1990ies. Up to that most of my music LPs and CDs stem from.
Guitar and bass amps I restored some of. My preference is Fender. But I have some old Dynacord amps too, especially also a reverb unit with tape loop. Of course all tube based. And over the last 6 years I restored a lot of vintage tube amps of a recording studio. These were Magnecord, Concertone, Ampex, Telefunken, RCA and others. Lot of rework, many caps and some resistors. Now it is all OK mostly and I can work on my own stuff again. During my time at hp I only had to do with semiconductor gear and computers. After retirement I started with tube based equipment again as I was used prior to hp. This is also reason to have old digital voltmeters because newer ones did not have the ranges up to hi voltage anymore. Now with electrical driven cars this might be necessary again in the future.
well spoken. For the young people sound modeling is the future. Also since the art of music changed. Much electronic stuff. Also real good music. But I am old school, so I leave it to them. I still stick with performers approx. to the 1990ies. Up to that most of my music LPs and CDs stem from.
Guitar and bass amps I restored some of. My preference is Fender. But I have some old Dynacord amps too, especially also a reverb unit with tape loop. Of course all tube based. And over the last 6 years I restored a lot of vintage tube amps of a recording studio. These were Magnecord, Concertone, Ampex, Telefunken, RCA and others. Lot of rework, many caps and some resistors. Now it is all OK mostly and I can work on my own stuff again. During my time at hp I only had to do with semiconductor gear and computers. After retirement I started with tube based equipment again as I was used prior to hp. This is also reason to have old digital voltmeters because newer ones did not have the ranges up to hi voltage anymore. Now with electrical driven cars this might be necessary again in the future.
Hi radiogaga,
That's so funny. My favorite guitar amplifiers are also Fender, not so enamored with Marshall as they only do crunch. You can get so much out of a Fender Twin -whatever model. Right now I am rebuilding a tube based Mc Curdy radio station stereo console for a friend. I've done a lot of gear for recording studios as well. Always interesting.
The newer Keysight meters are back to 1 KV + input voltage range. The 3457A and similar looking LCD meters had a 300 VDC maximum input range. THe newer 34401A (I had three) were back to the 1 KV + max input range. Then of course you do have the option of high voltage probes (with reduced accuracy). So the low voltage range limitations are long past, but the new meters are a bit dear.
That's so funny. My favorite guitar amplifiers are also Fender, not so enamored with Marshall as they only do crunch. You can get so much out of a Fender Twin -whatever model. Right now I am rebuilding a tube based Mc Curdy radio station stereo console for a friend. I've done a lot of gear for recording studios as well. Always interesting.
The newer Keysight meters are back to 1 KV + input voltage range. The 3457A and similar looking LCD meters had a 300 VDC maximum input range. THe newer 34401A (I had three) were back to the 1 KV + max input range. Then of course you do have the option of high voltage probes (with reduced accuracy). So the low voltage range limitations are long past, but the new meters are a bit dear.
Hi Chris,
you are right. The trend went backwords but not above 1kV DC aka 750V AC. Some of my old meters can take up to 1999V DC. An old analog handheld one is up to 5kV DC. 30kV probes I have some but are unhandy for measurments and I need them seldom since my TVs are all flatscreen now. The recording studio which explicetely records old school with tube based equipment had bought a big RCA mixer, I think it is 12 mic channels, everything only tubes. Was a hard long restoration process. Bad tube sockets, caps, some power resistors bad. Noisy stages. Now it seems to be OK but not used for every recording.
Hi radiogaga,
That is true enough. I was clear that 300 VDC suited a nice, clean safe lab environment, or maybe a school. Things get decidedly more dangerous out in the world. Reality bites, I wonder who at HP thought 300 VDC would be enough?
A tube console would certainly heat the area up! THey normally only use smaller outboard gear for that tube sound for certain instruments. The strips I've worked on normally get metal film and polypropylene upgrades simply to get the noise and distortion down while retaining that sound. At least the grid circuit resistors in order to get the noise down, leaving the plates will allow for the higher distortion if they want that.
Yes, it is a ton of work, I hope they appreciate the efforts! Even the early solid state consoles are a handful (Neve in particular).
That is true enough. I was clear that 300 VDC suited a nice, clean safe lab environment, or maybe a school. Things get decidedly more dangerous out in the world. Reality bites, I wonder who at HP thought 300 VDC would be enough?
A tube console would certainly heat the area up! THey normally only use smaller outboard gear for that tube sound for certain instruments. The strips I've worked on normally get metal film and polypropylene upgrades simply to get the noise and distortion down while retaining that sound. At least the grid circuit resistors in order to get the noise down, leaving the plates will allow for the higher distortion if they want that.
Yes, it is a ton of work, I hope they appreciate the efforts! Even the early solid state consoles are a handful (Neve in particular).
Hi anatech,
I don't know either what hp thought when designing a 300V max meter. Perhaps it was the trend to semiconductor and digital IC work, no tubes anymore. I have two of these multimeters which work very good. But in tube circuits (one musical amp from Dynacord, the Gigant works with 700V DC plate voltage) it is too dangerous to use these limited meters. Another meter was killed by tipping on a hv point accidently.
Yes, metalfilm and polypropylen insertion I did on some of these old 1960ies tube amps. On the other hand, the most noise comes from the first stage in a mic amp. Refitting this one with the better components by removing all the composite resistors gave only 3 dB noise improvement. But practically all caps were leaky and exchanging these without the resistors was often good enough.
Hi radiogaga,
That's fair enough. I normally see a greater s/n improvement, especially with a Mic preamp. This would also depend on the tube used. 12AX7A would be expected, or the much improved 6EU7. Later ones may use a nuvistor. Those things run HOT! I would expect DC heater supplies as well. Using newer Electroharmonix tubes would improve things as they are very quiet. Any of the New Sensor product out of Russia would be your best bet for low noise tubes.
-Chris
That's fair enough. I normally see a greater s/n improvement, especially with a Mic preamp. This would also depend on the tube used. 12AX7A would be expected, or the much improved 6EU7. Later ones may use a nuvistor. Those things run HOT! I would expect DC heater supplies as well. Using newer Electroharmonix tubes would improve things as they are very quiet. Any of the New Sensor product out of Russia would be your best bet for low noise tubes.
-Chris
Hi Chris,
it is true what you say. The mic preamp stage which I worked on used an old metal tube (can't say the type because I am on vacation and have no access to the schematics) so there was almost no chance to get better ones. The studio owner purchased some used ones and we tested all these. Half of them were worse than what we had. An new ones do not exist anymore. For the 12AX7 types there are good noise selected which you can get. Tubes from Russia were reliable and not too expensive. Chinese ones I do not like. There people had not so good experience, especially with power tubes in musical instrument amps. For the EL34 stuff I took always these from EH, very reliable. JJ was not so good to my experiene. And when EL34 need to work with 700V DC which means a swing to almost double only good tubes work long.