Dynaco ST-70 Integrated Stereo Tube amp Filter capacitor repair Tech Tip advice from D-Lab
ฝัง
- เผยแพร่เมื่อ 6 ก.ย. 2024
- Many of these amps have been coming thru the doors of my shop. Every one needs new filter caps. After 60 years of service, there is no need to test or hope they will get by for a few more years. Just change them. Use the highest quality possible, examples would be CE manufacturing or F&T. Dont cheap out or you will pay the price. These amp have served us all well. They deserve the best to ensure more decades of quality tube audio! If you do not feel comfortable performing this task, D-Lab is here for you! I promise professional results at reasonable cost. My shop is focusing on Dynaco/Marantz/Fender/Gibson/Johnson/National. Contact me with your needs. Reputation is everything.
![เปิดใจ พี่ญา คนรุม หลังทัวร์ลง หนักสุดในชีวิต!! l [Nickynachat]](http://i.ytimg.com/vi/2-OJZRtclro/mqdefault.jpg)
![Warhammer 40k: Space Marine 2 | เพื่อจักรพรรดิ ! [ตอนเดียวจบ]](http://i.ytimg.com/vi/4M0ckYMA4-U/mqdefault.jpg)
Those F&T Authenticaps caps are a lifesaver for us old tube-heads. Very highly recommended.
Agreed, an ounce of prevention = a Ton of cures. The grid on this side of the pond can vary from 220V to 250V from the wall sockets .As far as I am concerned you can set a bench-mark for your Sincerity which is a breath of fresh air these days. Thanks for sharing your experience with us.
The thick layer of dust on the top side kept making my OCD twitch 😂
Especially with that cheesy phenolic printed circuit board. It should be thoroughly cleaned of dust to prevent arcing, which can damage it beyond repair.
@@jonathanknight8251 to
@@gourangosutradhar2898 ot
Ja das. Geht
Was zuckt das lebt
Everything this man says here is good advice. He is right that Mark II and Mark III Dynaco amps have higher voltages than an ST70 on the B+ section of the quad cap in the power supply. Home line voltages when these amps were new was around 115-117 volts. I have seen line voltages as high as 127 volts in recent years. You have to multiply the difference in line voltage by four to get the voltage the quad cap sees. 550 volt quad caps are perfectly fine for a ST70. Several suppliers offer new replacement quad caps that are superior in every way to the originals. The biggest weaknesses these amps have today are the old caps and resistors.
Your advise is valid. There is almost 500V there. Some tolerance is needed. HV may be higher at startup and lower when tubes heat up.
Possible but the capacitor should have a higher surge voltage ratiing.
@@acoustic61 Caps from that era had working voltage (wvdc) and surge voltage ratings. Today, the rating IS the surge voltage.
Terry - your tech tip was spot on regardless of the outcome. Even 500v is too close for comfort. Good stuff
Missed the selenium rectifier procedure. Have one in a hh Scott 340b that needs to go.
I love my ST70. Mine looked a little worse when I got it so I did a complete teardown and rebuild on it leaving it in the stock configuration. Best sounding amp ever! Thanks for another spot on video Terry!
That puppy is gonna be LOUD. I love those Stone Age PCB’s! Finally got my own Snozersmous! Been putting it off but found a vintage 80 watt one on EBay with a HUGE brass tip that can be ground down. Lots of it is left. Man it makes SUCH a difference compared to the small 80 watt iron I was using for chassis. Does the job 10 times quicker! I LOVE it!!
Those Stone Age PCB’s are often scorched and can be problematic 🤷🏽♂️
Very good. Don't forget about changing that selenium rectifier.
You sir - have a great reputation. Thanks for your videos, they are well presented and your expertise is sincerely appreciated.
What a beauty Terry!... Except for the black beauties... Cheers!
You may not have got the response you were looking for, but the advice is equally important anyway and it's a worthy recommendation. Thumbs up as always, and I never tire of seeing ol' mate Snozz. :)
It never hurts to have a little more wiggle room on your filter caps. So as far as I'm concerned you weren't wrong. It is a valid tech tip.
Thanks! D-Lab. My Grandfather always told me you got to be smarter than the equipment you're working on. 🔌
Yes Sir, good advice, I may have to use that line
Liked that opening music! Nice Amp.
I think that the B-plus will be even higher after you substitute an efficient, high-current diode for the selenium rectifier.
Great video, you have a great reputation for many reasons. Plus, where else can you see a snozeramous?
Was getting all excited when I saw that cap change 🙃👍
I’m glad I watched this video and learned about F&T’s Authenticaps! I only know of their older blue dual-section radial, and black axial types..
Gotta love the stuff coming out of the cap can. Tasty! 😮
Awesome video D-Lab. Intro music was sweet. That tube amp was really nice.
Throw in old Snozzeramus and we got ourselves a D-Lab Classic.
Really good tech tips too. Thank you.
Thanks again Terry and happy holidays
Man I wish I could find someone like you to work on my old tube amp.
I am in complete agreement with you about not plugging in old equipment without first checking (or, better, replacing) electrolytic caps and taking a few other precautions before bringing it up slowly with a Variac.
The Mark 3 is a KT-88 / 6550 amp rated for 50 watts per channel. The ST-70 is a EL-34 / 6CA7 amp rated for 40 watts per channel and operates at a lower B+ voltage. 525 volts for a EL-34 / 6CA7 running class AB drastically shortens its life. Its B+ should not be much over 400 volts. It's all about plate dissipation.
I have a ST-70 to rebuild so this video is right on point for me! Thank you 😊
Never apologize for facts!
Excellent info, thanks for passing it on. Good reputation saves on advertising costs too!
hi terry, just wanted to let you know that i have been really enjoying your hamfest walkthrough videos. Im very envious as someone just getting into the hobby here in california and not having those kinds of events close by. Anyway i hope you continue to share your knowledge and humor for many years to come. Thanks.
i dug the intro music, great restore video too
The first thing l would of fine is clean the dust and scunge off the chassis. I work with a clean machine. No crud!
Great video
I had the same Exact experience with a set of mk3s. Idle was at 538v. Since I already installed ce distribution cans at 525v, I ended up installing single 30uf at 600v at the B+, then used the can cap for the other sections. My st70 peaks at 500v. I guess only the monoblocks have the high voltage issue.
I wouldn't trust CE Distribution caps. I think their QC is poor and I've heard of early failures.
@@acoustic61 I've been using CE can caps for years and have never had a single one fail. I've installed at least 50 of them in amps that I've serviced, from Dynaco to Fender, to McIntosh amps, and found them very reliable. Experience is better evidence than what you read or hear about on the internet.
@@stevelark9840 I had one with a QC issue and after apologizing they replaced it with another one with the same issue. I won't use or recommend them unless a customer insists on them for esthetics. Have also heard from a relaible source and well known builder that he's had early failures and won't them either. They're overhyped and expensive.
B+ would be a bit higher if the correct 5AR4 rectifier tube were installed instead of the 5V4 that’s in there. Though with today’s line voltages, the 5V4 will provide a bit of safety margin.
It has a Sylvania 5AR4 installed. The only original tube that survived
@@d-labelectronics The bulb looks very much like that of a 5V4 and not like that of a 5AR4. It would be interesting to plug another 5AR4 into the amp and see if B+ comes up a bit higher.
I never play around when soldering in a cap. Use propane torch on high.
Thanks Terry,
Always useful information.
"The ol' selenium RECTUM FIRE"......
Have to respect that .Peace Terry
Howdy.
Did I hear Rectum Fire ??? ROFL ...
Once I have got myself together I must make an appointment to a hearing doctor or possibly to a psychiatrist ...
Regards.
Selenium Rectum Fire made me laugh... I thought of Johnny Cash and the Ring of Fire and Preparation H at the same time!
Nice tube amp very christmas.
I'm wondering what it is about Portugal that makes it so popular with ghouls.
Great video - thank you, Terry!
With the tubes installed >500v. Without the tubes or open transformer lead (lessening the load), the voltage can creep up. Did you test without the tubes? Even at 490v I like the comfort zone of 550v. It gives me a nice false sense of security.
I want those two good Sylvanias!!!
I'm sure you've likely discussed this, but why not install an inrush current limiter, such as the CL-90. I find startup voltages are held somewhat in check by them, and they shave a few volts off the top, which can help when line voltages (where I live) hit 128VAC. What's your thoughts in general on them? I install them in almost every repair I do (of my own gear).
In-rush limiters are especially important if someone decides to bypass the GZ34 tube rectifier with diodes.
@@randyrobey5643 Not to mention replacing the Selenium rectifier with Silicon....only raises the voltage yet more. Short of a Bucking Transformer, which are critical for controlling the high voltages in certain amps such as the Heathkit W5M, the inrush will shave off 1-2 volts hopefully. I was wondering if there is an "audio" reason for not using them?
You're almost at 500Vs anyways, so 525V was a very good call!
Found a snoz at the thrift store last week, still in the original box. $10.00!
Good job Terry. Nice and thorough.
Yeah, you gotta preserve that fine patina layer of dirt and dust (aaaachooooo!).
Barn fresh love to dig into one
Good advice! Thanks.
Enjoyed the tube amp content!
Do a Carver refurb next.
I'm working on a Fisher 500C receiver. It has a selenium full rectifier for the negative bias power supply. If I replace it with a silicon diode bridge, I would think it will need some added resistance to bring the bias voltage in line. Is this the case?
I will leave the selenium in until everything is up and running, but it doesn't give me a warm fuzzy feeling leaving it in long term. Love the Dynaco stuff, I have a PAS-3 factory assembled preamp that needs recapping as well. Not using it, keep kicking that can down the road, future project. Love the vintage stereo tube videos, always learn something from you.
Yes, Its coming out as well as the black beauty caps
Are you doing any of the David Gillespie mods to that 500C?
@@acoustic61 Trying to keep it as original as possible.
So sad I sold mine, I do have a chromed chassis for a pre amp with most parts
wish this vid was way longer.
The 6L6GC on bottom left side is on a poor vacuum condition and needs to be swaped to a new one ...
Great job and excellent statement at the end! Just curious, where do you find the multi section can capacitors like that rated over 525 volts?
vacuumtubevalues.com/authenticap/
Where did you happen to get that F&T can capacitor? Never noticed on Mouser. Nice job!
vacuumtubevalues.com/authenticap/
👍
Many old circuit amplifiers
Love ya brother
Ótimo vídeo congratulações
v nice
Thanks for the video. Where do you order those cans from? Do you have a part number?
integrated amp?
You are so special it is sickening.
Nice video, but it's a power amp not an integrated amp.
But you didn't state your line voltage....your tip could still be valuable.
Glad to see you're using Authenticaps. I think the quality control at CE Distirbution is poor.