New guy. First post. Bias question.

I'm 60 and recently decided to get together a decent tube stereo system (within my means) so I can begin to enjoy vinyl again. I have a large LP/45 collection left over from owning a record store 25 years ago.

The power amp I went with was an RFTLYS from China. You can check one out on this eBay auction. The guts are point to point and it seemed pretty nice.

http://www.ebay.com/itm/RFTLYS-EL34B-x4-Tube-Integrated-Amplifier-Brand-New-/390511459779?pt=US_Home_Audio_Amplifiers_Preamps&hash=item5aec4bfdc3

The other night I decided that the thing just was missing something....bottom, presence, etc. *So I called Bob and ordered an ST 70. Shoulda done that first.

I had figured I'd sell the RFTLYS on eBay but then I thought I'd hate for the next guy to be disappointed. Now I'm thinking I've set the bias too low. I mostly know guitar amps and I know a too cool bias might make a guitar amp sound "thin".

The company in China suggested 30 mA for the bias. The guy at the local hi-fi shop said 30 mA. Running at 120 volts I have almost exactly 400 volts on the plates. So I set the 4 EL 34s at 29-30 mA. The Weber bias calculator says 38 is avg and 44 is hot. 31 is low. I know this site is referencing guitar amps so it might not even apply. I'm not a tech.

Where would you guys set the bias on this?

*Oh....I pulled the RFTLYS out of the system and re-installed my old Yamaha AVX 100U. It was a world of improvement. That's when I called Bob.

Thanks guys. Can't wait for my new ST 70.

I'd try 40 - 45mA for bias.

But looking at the pictures, bying 2 dynakit output transformers, cutting away the components and rewiring it to be a point-to-point wirec dynaco / vta / triode clone is perfectly doable although not costefficient. But if already have a couple of transformers it should be cost-efficient.

Thanks.
I have no plans to re-do the amp. I'm just wondering if I went too low on the bias.

The reason I haven't just tried this is that it's a pain to set the bias and I've already messed with it some but I guess that's what I'm going to have to do.

Dave, your experience should be a cautionary tale. Don't expect to save money buying a no-name Chinese amp on the internet.

ramon68 wrote:Dave, your experience should be a cautionary tale. Don't expect to save money buying a no-name Chinese amp on the internet.

I love my ST-120, but honestly the workmanship on the Chinese Amp linked looks top notch. I can't really get a feel for the Caps (hard to read) - but assuming they are reasonable - it should perform reasonably well.

Some suggestions (from one newbie to another):
1) Try adjusting the bias to .4
2) If you have the tubes, try changing the driver tubes to see if it impacts sound quality (it should)
3) You can change the power tubes and it will slightly alter you tone quality and power, but the drivers are usually the most impactful.
4) I'd look over the internals of the amp to make sure nothing is obviously loose from shipping, it looks like they are hand assembled so its possible something was knocked loose in shipping.
5) If you have the electronics know-how consider replacing the capacitors on the board with higher quality PIO Russian, or Muldorf caps.

I don't own a Chinese amp, but if I did, this would be the one I'd buy.

David

Thanks.
I think the tubes are okay. I got the EL-34's from Dougs Tubes. Nothing super expensive, just some recommended Rubys.
The 12AU7's are NOS 5693's (RCA, I think). I've tried several 12AX7's new, NOS, etc.

To be clear..the amp sounds okay, it just doesn't knock my socks off. The test record that convinced me that it didn't have quite enough was my original 45 of Shapes of Things by The Yardbirds. Just didn't get it. This old mono 45 should kick butt. When I swapped in the old Yamaha, the magic was back.

I'm going to disassemble everything tonight, re-install the RFTLYS and re-bias to 40 mA. If it sounds alot better then I go ahead and try and sell it with a good conscience.

I appreciate everyone's help.

most likely the recommendation for 30ma (which is too low for EL34s, should be 40-45ma) is probably due to the limitations of the power supply in the amp.
The power supply probably can't supply enough current to bias all the tubes at that point.  
Opposite is true for our VTA70 version of the ST70, since the original was designed to run the tubes way too hot  (50ma each).
I can hear NO difference between 40 and 50ma on a VTA70, and the power transformer and the tubes will last twice as long (maybe 80 years instead of 40!!)

I just saw the last post.

I just re-installed the Chinese amp and I'm waiting for it to heat up.

More in about 15 minutes.........

Okay, big difference.
I ended up at about 43 mA on each tube. The bottom and "presence" were much better but I'm betting some cap upgrades would make this even nicer. I'm glad I went ahead and ordered the ST 70 from Mr. Latino.
 
Here's an actual gut shot of my amp (if this works..I'm a new guy here).

I purchased a VTA ST-120 with all the upgrades plus an attenuators and the time delay relay. I can't be happier with this amp. It's driving Polk Audio LSiM 703's and the sound is phenomenal. I almost considered one of those Chinese amps and am happy with my decision to go with this amp. Personally I'd cut my loses and move on. No use sinking money into something that may have other problems.

Yeah, I'm just glad that now I'll be able to sell the Chinese amp knowing that's it right. It sounds pretty good. Right now I'm listening to Caravan's first LP (mint) and it sounds very nice. I might even keep it as a back up or something.

Can't wait to hear my vinyl with the ST 70.

I am so psyched to get back into listening to this great sound vinyl after 20 years of cds in cars, mp3 on the computer...blah..blah...blah.

Dave_in_Va wrote:Yeah, I'm just glad that now I'll be able to sell the Chinese amp knowing that's it right. It sounds pretty good. Right now I'm listening to Caravan's first LP (mint) and it sounds very nice. I might even keep it as a back up or something.

Can't wait to hear my vinyl with the ST 70.

I am so psyched to get back into listening to this great sound vinyl after 20 years of cds in cars, mp3 on the computer...blah..blah...blah.

Give this amp a couple of weeks to break in.  Put up the schematic if you can - the folks here are quite learned in the ways of Hollow State.

The Chinese guys were very nice and sent me a schematic in case I need any service. The warranty was cool but two way shipping between the east coast of the USA and China is kind of prohibitive for a $600 amp.
 
I doubt if it's kosher to post the schematic.

The build quality looks excellent for something in that price range. Let it break in before giving up ... you may have a sleeper there ...

Probably best to keep an eye on those transformers running that high over the suggested rating. Should be interesting to see if they run hot, or if the mfg is just ultra conservative on their ratings ...

The guy that sold it had to check with another guy and he was the one that said 30 mA. Cooler bias-longer tube life is the rule with guitar amps.. They may also be forecasting future complaints from non gear-heads about amps crapping out when it's really just a tube.

Listening top a mint copy of Curved Air Phantasmagoria. Sounds good.

You have to break the amp in. I'm sure it'll sound way better once it hits 100 hrs.

can't tell about the transformers, but the build looks good, and the photo is so good I could draw a schematic from that alone in about an hour

By the way, here is the link to the Weber bias calculator page.

http://www.webervst.com/tubes1/calcbias.htm

(I've got 388 volts on the plates according to my Weber Bias-Rite.)

Greetings Dave_in_VA from the other side of the states...

I agree with others who have suggested that you stay the course and give the amp time to burn in.

My son had a Woo Audio 2 headphone amp (he has hence upgraded) which is Chinese made. It is a beautiful looking unit. I was impressed with both the build quality and the sound of the amp. There is some quality stuff coming out of China/Hong Kong.

Let's not forget that there was a time when "Made in Japan" was considered poor quality merchandise. We all know how that has turned out!

I own a VTA modded ST-70 that I couldn't be happier with. The sound is as good as one can get at that price. I am sure that you will be happy with the unit from Bob.

Let us know how the two compare after you have given both some burn in time...

My new VTA ST-70 is arriving tomorrow. I'm pretty excited.

I'm currently using the Yaqin MS 12B tube phono pre-amp. It has two outputs, a .25V and a .7 V. I am currently using the .7 output into my RFTLYS as it sounded better than the .25. The instructions that come with the Yaqin are (to me at least) confusing:

2. Power Input* Socket (OUTPUT 0.25V)  *I assume they mean "Output"
   This signal output socket can be connected in the place of sound source input (INPUT) for integrated amplifier.

3. Signal Output Socket  (OUTPUT 0.7V)
   This signal output socket can be connected in the place of input socket for preceding stage of pure post-stage amplifier.

Soooo, when my VTA ST-70 arrives, which is the correct output to use on the Yaqin?

Thanks again for everybody's help and advice. For the record, the RFTLYS is sounding really nice since the re-bias and (I assume) a little more break-in time.

Whichever one works right with the gear mostly. I'd start on the high side at low volume. If that doesn't give the drive you need, go low ...

I'm told I'm crazy running a McIntosh MC2205 at .75 on my system, but hey ... it works nicely. Can't argue with that.

But they ARE right about the crazy part .... AHHAHHAHHAHAAAA!!!

Got my VTA ST-70!
Tweaked the bias and had it running in about 10 minutes. I could tell an improvement over the RFTLYS immediately. I guess the ST-70 will also benefit from a break in.

I think I may move the RFTLYS over to be the amp in my TV/DVD system. I'll need to do something about a DAC. I no NOTHING about DACs unfortunately.

I guess my next step is to upgrade the Yaqin MS 12B pre-amp.

I'm pretty excited. This is so cool. Thanks for the help and advice.

... and Dynaco has more vowels than RFTLYS, so the vocals should be easier to understand ...  

Any idea what RFTLYS stands for? Or how it's pronounced? Or what the hell they were thinking when they named it?

Might be fun to try swapping tubes between the amps ... see if a better tube helps the FRTLYS any.

It does look like a real decent amp though. Rather than flip it or stick it in the corner, I'd be tempted to do some upgrades and see what happens ... if nothing else, it'd be good practice for when you get around to upgrading the Dynaco ... nudge nudge ...

I have no idea where the name RFTLYS came from.
You know, it sounds pretty good since the re-bias. The ST 70 is better though.