Yaqin MC-84L Tube Stereo Amplifier Review

[Blumlein 88]

In theory, yes, but they would have to hire a competent tube engineer. Their market doesn't care- "Ooooh, it's got tubes and it's cheap! Sold!"

Do you mean to tell me starved plates aren't really high end hifi? And I've seen tubes glow purplish blue even if it wasn't exactly led blue.

 

[SIY]

Do you mean to tell me starved plates aren't really high end hifi? And I've seen tubes glow purplish blue even if it wasn't exactly led blue.

You can actually make a good starved plate stage if you know what you're doing. I built one after seeing a talk and having a long discussion with Tim DeParavicini and it worked shockingly well.

The key phrase is "if you know what you're doing."

 

[Blumlein 88]

You can actually make a good starved plate stage if you know what you're doing. I built one after seeing a talk and having a long discussion with Tim DeParavicini and it worked shockingly well.

The key phrase is "if you know what you're doing."

Well that is interesting. So how well is shockingly well?

 

[SIY]

Well that is interesting. So how well is shockingly well?

I don't have my lab book with me (I'm in Cleveland to see a football game), but something like -80dB distortion at 25VRMS out. 0.2mA through a 6DJ8 cascode.

 

[DanielT]

OK – let me try to repeat my question in a more simple form:

Which model would be the right one for somebody who is looking for an integrated tube amp that costs no more than $600?

To test a tube amp. Used tube amp in that case buy well-known brand and model. That so you can buy and sell at roughly the same price. Old amplifiers may need service, repair and replacement of electronics. Can be expensive if you hand it in to a professional repairman who charges by the hour. Just so you weigh it into the whole thing.

I had a quick look at a Swedish used site. Just as an example of what you can find. If 17.5 watts is enough for you, then a integrated Dynaco SCA-35 tube amp, which appears to be in good condition, for $360? A Dynaco SCA-35 might be for sale where you live?

I haven't checked the used prices on that SCA-35 model, but I guess they are around $350. To get an idea of reasonable prices research it via for example Hifishark and or ask here at ASR.

Dynaco SCA35 Stereo Tube Amp

Integrerad Rörförstärkare Dynaco SCA 35 Med Rör Riaa . Sitter Tight Matchade JJ EL84 i Slutsteget . Originaltrafos, 230V. Bilder mailas vid intresse.

hifitorget.se

Dynaco SCA-35 [English]

Dynaco SCA-35, an integrated amplifier listening test on TNT - Internet HiFi magazine

www.tnt-audio.com

Edit:
Tube amp friendly at least 8 Ohm speakers, with non wildly fluttering impedance and preferably with at least 90dB sensitivity and you are ready to fly away with a 17.5 watt tube amp. Especially if you let a subwoofer take over everything below 80-100 Hz at the same time as Dynaco SCA-35 does not work at any of these low frequencies (HP-LP filter needed).
That IF you don't love playing music at a crazy high level.

 

[SIY]

SCA-35 is a fine amp, the only issue may be finding replacement input tubes (7199).

 

[DanielT]

SCA-35 is a fine amp, the only issue may be finding replacement input tubes (7199).

Thanks for the input SIY. That proves my point. Ask the experts here at ASR, for example, what you should think about before making a purchase.

Actually, I see these old tube amplifiers as fun hobby projects for enthusiasts. To fix and service. Maybe even upgrade. The fact that they can then be listened to is a nice bonus.

If this Dynaco SCA-35 Project in the link below rendered in a better sound, better performance I don't know. Regarding finding replacement input tubes (7199).
Maybe Troutbear have solved it by:Switching to the new amplifier boards also entails a change in driver tubes (7199 -> 6GH8A / 6U8A). New amplifier boards, then we are onto something different in and of itself.Good, bad, better possibilities with the choice of tubes and so on? I have no idea but on the other hand I'm not going to buy an old tube amp and then repair and upgrade it. I leave that to technically knowledgeable people.

In any case, it looks nice with new inputs and speaker connectors:

Dynaco SCA-35 Project

"think I would start by investigating the possibility of swapping in ST-35 amplifier boards as they are already designed for an appropriate level of gain without the tone controls. I have seen references to the idea here and there online, but have not seen any documentation, projects, or even...

hifihaven.org

 

[raindance]

SCA-35 is a fine amp, the only issue may be finding replacement input tubes (7199).

Plus the input sensitivity is about 10x higher than you need for CD or other 2 volt sources, so to get decent tracking and usable control range from the volume control you'll need to add a divider to one of the inputs. I do suspect that this is why people think tube amps are so powerful though, "look, my volume is barely on and it's so loud!".

 

[biker29]

You were asking something similar to, "looking for a reliable car and that you want it to be a Volkswagen".

If you want to try the tube sound, you might as well buy this as it colors the sound enough you might hear something 'tubey'.
If you want a clean sounding tube amp skip it and buy a clean sounding non tube amp.

If you just want that tube visual look try one of the Parts Express, Dayton amps that use a tube pre-amp like these 2. They have more features and are more powerful.

Dayton Audio HTA200 Integrated Stereo Hybrid Tube Amplifier 200 Watts

Dayton Audio HTA200 Integrated Stereo Hybrid Tube Amplifier 200 WattsDayton Audio HTA200 Hybrid Tube AmplifierThe perfect solution to bring the rich sound of a tube amplifier to your home audio setup; the innovative design of the HTA200 combines the best of both worlds – the classic sound of...

www.parts-express.com

Dayton Audio HTA100 Integrated Stereo Hybrid Tube Amplifier 100 Watts

Dayton Audio HTA100 Integrated Stereo Hybrid Tube Amplifier 100 WattsDayton Audio HTA100 Hybrid Tube AmplifierThe perfect solution to bring the rich sound of a tube amplifier to your home audio setup; the innovative design of the HTA100 combines the best of both worlds – the classic sound of...

www.parts-express.com

Tube amps usually refer to amps with Tube output stages. These amps have a tube driver (preamp section) and solid state amplification. If you want tube sound the amp section needs to be tubes.

 

[Timmy]

If you want tube sound the amp section needs to be tubes.

OK ... Speaking about integrated stereo tube amps – can I simply tell from the number of installed tubes of a given device that this could be a fully tube driven amp or not?

 

[DanielT]

To test a tube amp. Used tube amp in that case buy well-known brand and model. That so you can buy and sell at roughly the same price. Old amplifiers may need service, repair and replacement of electronics. Can be expensive if you hand it in to a professional repairman who charges by the hour. Just so you weigh it into the whole thing.

I had a quick look at a Swedish used site. Just as an example of what you can find. If 17.5 watts is enough for you, then a integrated Dynaco SCA-35 tube amp, which appears to be in good condition, for $360? A Dynaco SCA-35 might be for sale where you live?

I haven't checked the used prices on that SCA-35 model, but I guess they are around $350. To get an idea of reasonable prices research it via for example Hifishark and or ask here at ASR.
View attachment 401951View attachment 401952View attachment 401953View attachment 401954View attachment 401955

Dynaco SCA35 Stereo Tube Amp

Integrerad Rörförstärkare Dynaco SCA 35 Med Rör Riaa . Sitter Tight Matchade JJ EL84 i Slutsteget . Originaltrafos, 230V. Bilder mailas vid intresse.

hifitorget.se

Dynaco SCA-35 [English]

Dynaco SCA-35, an integrated amplifier listening test on TNT - Internet HiFi magazine

www.tnt-audio.com

Edit:
Tube amp friendly at least 8 Ohm speakers, with non wildly fluttering impedance and preferably with at least 90dB sensitivity and you are ready to fly away with a 17.5 watt tube amp. Especially if you let a subwoofer take over everything below 80-100 Hz at the same time as Dynaco SCA-35 does not work at any of these low frequencies (HP-LP filter needed).
That IF you don't love playing music at a crazy high level.

Popular? Apparently. I thought I'd check what the seller wrote in the ad but it was now sold (nope I haven't bought it).

So there we have an example. An ad that was only out for a few days and then that Dynaco SCA-35 gets sold.

With the right price, you can sell anything, anytime. Who bought that Dynaco SCA-35? Maybe someone who wants to test a tube amp? Who knows, that person might be happy with it and keep it for years. Who knows, he (not likely she) might sell it because he thinks it has too little power for his low sensitive speakers. Who knows ...and so on. What I do know, however, is that IF this person sells it, he will get as much, maybe a little more, for it than what he bought it for.

Buy well-known brands, well-known models. Find out reasonable used price then just buy and test.

The ad was not found

Edit:
I missed it, but checked now. It was sold in one day.

 

[mhardy6647]

I don't have my lab book with me (I'm in Cleveland to see a football game), but something like -80dB distortion at 25VRMS out. 0.2mA through a 6DJ8 cascode.

Space charge, yes? Even in a non-purpose-built space charge tube.
PS Since confession's good for the spirit: I am fascinated by the latter.

EDIT: PPS: Enjoy the game!

Space Charge and Other Low-Voltage Tubes

Tube projects don't always require lethal voltages! Some tubes were designed to run at 12V. Others were not but work well anyway at B+ down to four volts.

www.junkbox.com

 

[SIY]

Space charge, yes? Even in a non-purpose-built space charge tube.
PS Since confession's good for the spirit: I am fascinated by the latter.

EDIT: PPS: Enjoy the game!

Space Charge and Other Low-Voltage Tubes

Tube projects don't always require lethal voltages! Some tubes were designed to run at 12V. Others were not but work well anyway at B+ down to four volts.

www.junkbox.com

Nope, plenty of volts, just very few milliamps.

 

[mhardy6647]

Nope, plenty of volts, just very few milliamps.

ahhh!

 

[Timmy]

Just looking around ...

Under the brandname »dynavox« one can find no less than seven different integrated tube amp models. The VR-20 seems to perfectly fit into the Yaqin MC-84L price range:

Dynavox: VR-20 Stereo-Röhrenvollverstärker

dynavox-audio.de

 

[biker29]

OK ... Speaking about integrated stereo tube amps – can I simply tell from the number of installed tubes of a given device that this could be a fully tube driven amp or not?

A fully tubed stereo amp would have at least 3 tubes. One driver tube like 12AX7 and 2 output tubes like EL34/KT88/6BQ5. An amp like this will have 5 to 25 watts per channel. The term hybrid usually means tube driver and solid state output. Also you are not likely to find any 100 watt amps for less than $1000 even used.

 

[Timmy]

A fully tubed stereo amp would have at least 3 tubes.

That is per channel I guess? Or total?

 

[DanielT]

Just looking around ...

Under the brandname »dynavox« one can find no less than seven different integrated tube amp models. The VR-20 seems to perfectly fit into the Yaqin MC-84L price range:

Dynavox: VR-20 Stereo-Röhrenvollverstärker

dynavox-audio.de

Here a repair thread with Dynavox VR-20. The pictures and schematics plus what is said in the thread can perhaps give indications to a tube knowledgeable about the quality of the construction and the quality of the electronics in Dynavox VR-20

That's the schematics for VF70, identical to VR20, but VR20 has 6P6P instead of EL34.

Röhrenverstärker Reparatur, ein kanal dumpf - mosfetkiller-Forum

Ich fand kürzlich ein Dynavox VR20 Röhrenverstärker basierend auf einer 6F2 als Vorstufe und je einem 6P6P paar als Endstufe. Nachdem ich an den Ausgängen or…

forum.mosfetkiller.de

 

[AnalogSteph]

That is per channel I guess? Or total?

Per channel. EL34 is a single pentode, and for anything more than very pedestrian output power (think 2.5-3 W typ), you really do want a push-pull output.

 

[EdW]

That is per channel I guess? Or total?

Here’s a schematic of the Mullard 5-20, a quality 20+ watt EL34 push pull design approx 0.03% THD at 20W.
The GZ34 rectifier could of course be replaced with semiconductor diodes with perhaps a small reduction of the mains transformer secondary voltage. In the 60’s I made a few of these using ex UK Admiralty surplus WW2 mains transformers, chokes and paper smoothing caps (superb quality!). I still have the first amp and the sound quality was very good when I last fired it up.
KT88 designs could achieve nearer 50W as I recall. I made a couple for friends who wanted a good amp for guitars. No schematic - sorry.