I just finished building my first DYI tube amp, a Dynaco ST-120 from Bob Latino.
The first time I turned it on there was a fairly loud pop or snap sound, which occurred after roughly 20 to 30 seconds (I can't recall the timing). How can I determine if it was a turn on thump or if there's an actual problem that requires troubleshooting.
I'm just afraid to turn it on for fear that it could damage other parts that are currently fine.
your help is much appreciated. I'll probably hear back from Bob tomorrow but I was hoping someone out there might have a response in the mean time.
kind thanks,
Eddie
The first time I turned it on there was a fairly loud pop or snap sound, which occurred after roughly 20 to 30 seconds (I can't recall the timing). How can I determine if it was a turn on thump or if there's an actual problem that requires troubleshooting.
I'm just afraid to turn it on for fear that it could damage other parts that are currently fine.
your help is much appreciated. I'll probably hear back from Bob tomorrow but I was hoping someone out there might have a response in the mean time.
kind thanks,
Eddie
After 20-30 s tubes start to conduct. Remove the tubes and make voltage measurements. Start by PSU.
If you are using a tube rectifier GZ34/5AR4 the big amps are hard on them. You should add the "diode mod" using the newer faster & quieter UF4007 over the IF4007 for a few cents more.
They will take a good part of the load off the tube still keeping the great slow warm up that only that tube provides for the rest of the tubes and caps which helps their life plus it doesn't hurt the sonics.
Never run a tube amp without speakers or a load or you risk the transformers.
Also let the tubes cool off for a good 5 minutes or more (depending on room temperature) before restarting a tube amp when testing etc. or you also risk the tubes etc.
You probably have been on their Forum page:
tube rectifier diode mod
You can also just solder the SSS diodes in series on the Power Supply Transformer Secondary B+ wires that go to pins 4 & 6 of the tube rectifier. Use heat shrink tubing for support and to prevent shorting. You can cover the diodes and make sure to observe the correct polarity of the diodes. The banded end for both diodes is soldered to the tube rectifier at pins # 4 & 6 as shown.
They will take a good part of the load off the tube still keeping the great slow warm up that only that tube provides for the rest of the tubes and caps which helps their life plus it doesn't hurt the sonics.
Never run a tube amp without speakers or a load or you risk the transformers.
Also let the tubes cool off for a good 5 minutes or more (depending on room temperature) before restarting a tube amp when testing etc. or you also risk the tubes etc.
You probably have been on their Forum page:
tube rectifier diode mod
You can also just solder the SSS diodes in series on the Power Supply Transformer Secondary B+ wires that go to pins 4 & 6 of the tube rectifier. Use heat shrink tubing for support and to prevent shorting. You can cover the diodes and make sure to observe the correct polarity of the diodes. The banded end for both diodes is soldered to the tube rectifier at pins # 4 & 6 as shown.
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My guess is component failure,
Possibly a resistor. Can you post a circuit diagram? (or a link to one)
How much experience do you have testing and making voltage measurements?
Make sure the power supply caps are discharged before you touch anything!
Regards
M. Gregg
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1) I have no experience testing & making voltage measurements but I do have a multimeter and I somewhat know how to use it
2) how do i make sure that the power supply caps are discharged??????????
3) yes, that link to the ST-120 is the right one
thank you very much for your help
Bob Latino doesn't sell Dynaco amps. He has them made from some modern source. The Dynaco ST120 is a transistor amp made 1966-1972. It is a free country but I have my opinion and using these words for a completely different product is a waste of everybody's time. Buy *****ese sourced **** parts, get *****ed on. I don't know where Mr. Latino's parts come from but I'll take small bets that they don't come from Philidelphia or New Jersey where the Dynaco transformers were wound. The transistor dynaco ST120 is a mediocre sounding amp but mine doesn't pop at turn on.
You discharge the power supply caps by making a tool of an old multimeter test probe from a meter with a 600 volt scale, a 600 v rated wire with an aligator clip lead on one end, and a10 watt resistor with solder tabs instead of floppy wires. You solder the two leads to the resistor, and cover the resistor with heat shrink tubing. You attach the alligator clip to power supply center, usually the speaker return line, and touch the probe to the other cap terminal. Use 600 v rated wire because tubes have caps holding 450 VDC or higher. I buy my high voltage rated hookup wire at tubesandmore.com or triodeelectronic.com, although the excessively fat THHN industrial wires are 600 v rated.
Did you read the high voltage for newbies sticky thread above? You need to obviously.
If you do the solid state high voltage rectifier trick mentioned above, you had better put a negative temperature coeefiicient resistor in the AC supply line to cut the turn on surge to the tubes. Or build a timer circuit to put a resistor in the transformer primary, then short across it with a relay after time is up. One source of NTC resistors is the GE line of CLxx parts sold by Newark.com and Mouser.com. A CL-70 might work, with its 4 amp rating. If your amp draws less than 3 amps AC current maybe use a CL-80. BTW the CL-101's I bought last year were made in USA, if anybody wants to buy a product that is consistently made to specification rather than inexpensive.
You discharge the power supply caps by making a tool of an old multimeter test probe from a meter with a 600 volt scale, a 600 v rated wire with an aligator clip lead on one end, and a10 watt resistor with solder tabs instead of floppy wires. You solder the two leads to the resistor, and cover the resistor with heat shrink tubing. You attach the alligator clip to power supply center, usually the speaker return line, and touch the probe to the other cap terminal. Use 600 v rated wire because tubes have caps holding 450 VDC or higher. I buy my high voltage rated hookup wire at tubesandmore.com or triodeelectronic.com, although the excessively fat THHN industrial wires are 600 v rated.
Did you read the high voltage for newbies sticky thread above? You need to obviously.
If you do the solid state high voltage rectifier trick mentioned above, you had better put a negative temperature coeefiicient resistor in the AC supply line to cut the turn on surge to the tubes. Or build a timer circuit to put a resistor in the transformer primary, then short across it with a relay after time is up. One source of NTC resistors is the GE line of CLxx parts sold by Newark.com and Mouser.com. A CL-70 might work, with its 4 amp rating. If your amp draws less than 3 amps AC current maybe use a CL-80. BTW the CL-101's I bought last year were made in USA, if anybody wants to buy a product that is consistently made to specification rather than inexpensive.
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Read ALL of the following..if you are not confident get someone to help who is an engineer.
I take no responsibility if you follow this its up to you!
Test for dead,
Make sure your meter leads are in good condition and keep your fingers behind the guards.
Set your multi meter to a range higher than the supply volts.
And use the DC scale. Make sure your meter is working by measuring a battery or DC source..then keep you hands OFF the CHASSIS. Support the amp so it wont move then..
Measure across the supply caps. If you get 0 V then they should be dead.
Never touch anything after power off without doing a test for dead.
Remember your meter will not show anything if its on the AC scale when you measure DC. So you need to know if what your measuring is AC or DC.
So do some tests with the equipment off first. (and unplugged from the mains).
The first thing to do is,
make sure the power supply caps have no voltage on them. Then check to see if there are any voltage settings for the mains input. Is it correct!
Then check all your components are in the correct place and polarity(direction).
Then check to see if you can see anything obvious while checking all the components.
__________________________________________________________________
If everything looks OK remove the rectifier tube and check voltages from the mains Tx and that all tube heaters light up.
Now you need to know if the bias supply is working because if the bias is not working you will drive the output tubes into full conduction.
If you get to this point post your values and results of what you find in a clear list like this
heater voltage is ...Volts
AC HT (B+)winding volts are....volts
Etc and we will be able to direct you further..without the rectifier tube in circuit you should get no B+ unless you have diodes across it or are using a diode bridge. Never assume the B+ is off or dead always test..one mistake and it could be serious. Having said all that its possible to do this with care!
The next step will be based upon your results..good luck! (Don't drink before doing this 😀) Happy new year!
Regards
M. Gregg
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I agree with the above comment,
About using the name of a SS amp with some tube circuit. Its not a good Idea!
However this seems to be the situation..🙂
Hopefully its just a standard tube circuit!
Once we have some data its should be standard fault location..even if its just to verify everything is OK.
NB don't run the amp without a load connected across the speaker connections.
Regards
M. Gregg
About using the name of a SS amp with some tube circuit. Its not a good Idea!
However this seems to be the situation..🙂
Hopefully its just a standard tube circuit!
Once we have some data its should be standard fault location..even if its just to verify everything is OK.
NB don't run the amp without a load connected across the speaker connections.
Regards
M. Gregg
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Bob Latino is selling kits from Roy at tubes4hifi.com. I used their driver boards for my Mk III clone and am happy with them. Bob and Roy both use made in USA transformers, which are probably the same Chicago manufactured Dynaco transformer clones that you can buy from triodeelectronics.com. I like those transformers, and I think even Pete M. used them in a project or two, without complaint.
The name may be unfortunate, and the details on the website are few, but I suspect that the ST120 is two modernized Mk IIIs on an ST70 chassis. No reason for it not to sound just fine - or at least Mk IIIish. Probably not sublime, but should be a nice amp - much better than ****ese ****.
If the OP has not heard back from Bob, he should try Roy. Roy seems to have a day job, so be a tad patient. When I needed some advice a few years back, Roy was very professional and helpful.
Good luck, and enjoy your build.
As mentioned it is a good idea to do the voltage check on everything first to make sure all is okay, but I'm pretty sure the problem is the modern tube rectifier 5AR4/GZ34 can't really take the high load of big amps from lot's of reading on these big Mother's or Papa's of the most popular tube amps. They are marginal at it so you might have heard it arcing. Some production ones are better than others, but in all they won't last.
The SS Diode Mod won't hurt the Slow Start Up that the 5AR4/GZ34 is famous for and that's probably a big reason they kept it.
I bet doing the Mod will totally solve the problem mentioned!
Some put in the SS replacement and like it better sonically, but as mentioned it might be a good idea to add the delay circuit tubes4hifi sells if that is done though for better tube life etc.
Eddie maybe try cheap or throw away speakers when first testing something out new.
From pics I've seen I'm pretty sure the amp has the CL's to help things as STD equipment.
In all really nice amps!
The OPT transformers for Tubes4hifi and Triode are made by two different US companies in the US with the highest of reputations on the forums and from those I've talked to that have used them.
The SS Diode Mod won't hurt the Slow Start Up that the 5AR4/GZ34 is famous for and that's probably a big reason they kept it.
I bet doing the Mod will totally solve the problem mentioned!
Some put in the SS replacement and like it better sonically, but as mentioned it might be a good idea to add the delay circuit tubes4hifi sells if that is done though for better tube life etc.
Eddie maybe try cheap or throw away speakers when first testing something out new.
From pics I've seen I'm pretty sure the amp has the CL's to help things as STD equipment.
In all really nice amps!
The OPT transformers for Tubes4hifi and Triode are made by two different US companies in the US with the highest of reputations on the forums and from those I've talked to that have used them.
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Thank you all for your help and support. I can't thank you enough.
And thanks to Bob Latino, the ST 120 is up and running now. I was actually surprised that he was replying so quickly to my emails to him (even though some emails from me were sent around 1:30am on a Sunday night). Then he called me today and I got help on a couple phone calls. I use to sell Conrad Johnson, Martin Logan, B&W, Krell and more for eight years and was in the Hi Fi business for 10 years (until 1997) and I have never seen such responsive customer service.
Too early for a comprehensive review but I'll write one up on the ST 120 to share my opinion of several things soon.
For now, I'll just say that the amp sounds amazing and the customer service has exceeded my expectations, so far.
Bob immediately mailed me two replacement resistors because one of them blew and I'm pretty sure it was something I did wrong that caused a short. I think a wire might have extended a hair to far through the driver board and might have been touching the chassis on the other side.
with my experience so far, I would definitely recommend doing business with Bob Latino. I must admit, I was a bit uncertain and apprehensive but now I realize that I made the right decision due to Bob Latino's responsiveness and how he makes himself so available to clients.
Eddie
And thanks to Bob Latino, the ST 120 is up and running now. I was actually surprised that he was replying so quickly to my emails to him (even though some emails from me were sent around 1:30am on a Sunday night). Then he called me today and I got help on a couple phone calls. I use to sell Conrad Johnson, Martin Logan, B&W, Krell and more for eight years and was in the Hi Fi business for 10 years (until 1997) and I have never seen such responsive customer service.
Too early for a comprehensive review but I'll write one up on the ST 120 to share my opinion of several things soon.
For now, I'll just say that the amp sounds amazing and the customer service has exceeded my expectations, so far.
Bob immediately mailed me two replacement resistors because one of them blew and I'm pretty sure it was something I did wrong that caused a short. I think a wire might have extended a hair to far through the driver board and might have been touching the chassis on the other side.
with my experience so far, I would definitely recommend doing business with Bob Latino. I must admit, I was a bit uncertain and apprehensive but now I realize that I made the right decision due to Bob Latino's responsiveness and how he makes himself so available to clients.
Eddie
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