Sorry, don’t know what you have been listening too but that is not at all how my GM70 amp sounds and I have owned a number of very good SETs with all different tube types (300b, 2A3, 6c33c, 813, T100, GM70, EL34).
What are some great 300B SET amps $5-7K?
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The only explanation I have apart from PSU undernourishment or insufficient output transformer quality is that the life expectancy of GM70 is limited in the sense that they will "work" for thousands of hours, but tend to drift off spec after about 1'000-1'500 hours - enough that Lamm, for example, recommends replacing them every one and a half years. Amplifon solves this problem using an automated biasing circuit with an intentionally narrow window on startup - it'll simply refuse to play once the GM70s drift off spec.
(Edit: I know people whose GM70s have been playing just fine for thousands of hours, so it may be that vintage comes into play - GM70 were produced until the early 90s, and build quality and quality control may no longer have been up to earlier standards).
Greetings from Switzerland, David.
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According to Lamm, there is a 50% failure rate of the tube and he would have to go through another 25% of the tubes he received from Russia to meet his standards.
Good information here! I probably not look for GM70 with the answers posted here. I myself was considering Finale 300b monos. $5-7k is my price range too! My other choices are Canary Audio, Cary Audio, Sofia Electric & Audio Note Kit 300b. What I really want if I could afford it is either the Jadis i300, Audio Note Tonmeister or NAF 2A3.
I wouldn’t look for GM70 beneath a certain price range either (nor any jumbo style or other transmission tube) for the simple reason that power supplies and high-quality output transformers are of paramount importance, and the higher the output power, the more artisanal and expensive. If it has to be 300B and in this price range, I’d personally be looking at Decware, but the waiting list may be about four years now (a consequence of direct sale at an exceptional quality/price ratio).
Having said that, depending on where you’re located, you might be able to find a used Amplifon SET42, in which case I’d look no further.
Greetings from Switzerland, David.
the 6c33 was used as a series voltage regulator in the radar of the mig jet believe me they were very reliable. I have no idea how good the newer production of this tube is ,hard to find today old stock production. I can only say that the tube sockets are exposed to a lot of heat, and there is big potential for errors.before I put a new tube in, I check the sockets
I echoed the same concerns about GM70 above: reported problems may be entirely due to late 80s/early 90s production, if not dumping of lower graded tubes in the mid-nineties.the 6c33 was used as a series voltage regulator in the radar of the mig jet believe me they were very reliable. I have no idea how good the newer production of this tube is ,hard to find today old stock production. I can only say that the tube sockets are exposed to a lot of heat, and there is big potential for errors.before I put a new tube in, I check the sockets
Your point about Teflon sockets: no first-hand (negative) experience, but heard the same before.
Again, there’s an informative JAC Music article on the 6C33 as well:
http://www.jacmusic.com/techcorner/ARTICLES/English/Portraits/6C33/index.html
Greetings from Switzerland, David.
I would agree that vintage ceramic is the way to go … with one exception, Jakeband are hand made out of Italy and utilise very high quality materials.I can only say that the tube sockets are exposed to a lot of heat, and there is big potential for errors.before I put a new tube in, I check the sockets
-Sockets material: Virgin Teflon
-Pins: Copper Tellurim
-Pins coating: gold or silver plating (nikel free)
New production is terrible, according to Vlad Lamm anyway. RIP.the 6c33 was used as a series voltage regulator in the radar of the mig jet believe me they were very reliable. I have no idea how good the newer production of this tube is ,hard to find today old stock production. I can only say that the tube sockets are exposed to a lot of heat, and there is big potential for errors.before I put a new tube in, I check the sockets
Concur … with any of these valve types as OPT’s you tend get what you pay for with the quality of Iron and capacity of the PS Tank
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Don't forget these tubes make easy 250-270°C heat at the bottom, teflon melts at 320°C I didn't want to say more about the topic.
I never had a problem with the breadboard projects that I built Stephan however I was running on the conservative side , Ale Bartola has been using them for years … the Teflon in the Jakeband sockets are particularly hard and dense which may be playing its part perhaps.Don't forget these tubes make easy 250-270°C heat at the bottom, teflon melts at 320°C I didn't want to say more about the topic.
GM-70 – Bartola® Valves
www.bartola.co.uk
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Thank you David for your suggestions! Decware seems great value! But 4 yrs is long time!
I will google Amplifon as never heard of that amp!
I won't even argue with you. Everyone has their preferences and this is not a subject for debate, it should be respected. The article at the link tells only about the power of the tubes, there is no information about the sound properties.
I think that the 811A tube is really worthy of attention, but it was never mentioned here. This tube is not liked by manufacturers due to the difficulty of implementing the class A2 mode, the plate cap and the need to supply the heater with direct current. But it has excellent sound properties and a huge efficiency. With a heater consumption of 25 W and 45 W plate dissipation, the output power of the SET amplifier can be 20-22 W.
Sorry but you made some rather objective characterization about sound properties that you believed to be from the tube…not a discussion of preference. Both Acoustics guru and I disagree with this characterization due to direct experience with the tube and in designs wher it just doesn’t sound as you describe.
What GM70 amplifiers are you referring to? I mentioned two that patently do NOT sound “grainy”, “brutal” or anything such, but on the contrary are among the best-sounding SET amps I’ve heard, but you referred to ten or more that share an apparently tube related graininess etc. I’d be curious what brands those might be. I couldn’t even list ten commercially available GM70 amps. Please enlighten us! Thanks!
Greetings from Switzerland, David.
It depends a lot on how the tube will be used. The 6C33 was not designed to be used as an audio tube. In order to be used in such application we need to burn in and select them.
The same for many other tubes - many manufacturers claim similar rejection numbers for other types of tubes.
The good point was that not very long ago we could get boxes of russian 6c33's at around 5 euros each tube ...
This is your impression, I have a different opinion. My friends make
https://audiolot.com.ua/index.php?route=product/product&path=59&product_id=54
Therefore, I know the subject well.
They have 2 options: 30W and 40W. I would not include them in my audio system.
I participated in several screenings and had the opportunity to see and listen to many different devices. I don't remember the names of the things that don't impress me, look at the reviews from the last Audio Video Show in Warsaw, you'll definitely find GM70 amplifiers there.
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