New ST-70 has an odor

Just picked up what looks like a new ST-70. It was built from a Dynakit Parts kit. After running it for a little while I noticed a strong smell coming from the amp. Kind of like an electrical smell. I checked the bias and it was a bit high at 1.65. I wouldn't think this would cause the odor. Again, it looks new & I don't know the hours on the amp. Is this normal? Are there some voltages I should check? Thanks!

-Jeff

Hi Jeff..
By chance, would you have a Serial Number for this kit?

This would be stamped on the manual front cover and also on the sales receipt assuming you received these with the amp.

As far as the smell...Bias setting as a you stated was much too high although it's hard to say if this was the cause. I would go through a voltage test comparing these to the manual voltage specs. I would also double check the builder's wiring. Aside from the odor....Does the amplifier operate and sound OK to you?

Kevin @ Dynakit

Any chance that the power transformer has recently been re-painted and you are smelling solvents outgassing from partially cured paint?

DynakitParts wrote:Hi Jeff..
         By chance, would you have a Serial Number for this kit?

This would be stamped on the manual front cover and also on the sales receipt assuming you received these with the amp.

As far as the smell...Bias setting as a you stated was much too high although it's hard to say if this was the cause. I would go through a voltage test comparing these to the manual voltage specs. I would also double check the builder's wiring. Aside from the odor....Does the amplifier operate and sound OK to you?

Kevin @ Dynakit

Kevin,

unfortunately I did not get the manual or receipt.  Seller says it was built 5 months ago.  It does sound good.  Can I check the build against the Dynaco ST-70 manual?  The build looks pretty good but I'll check everything out.  Thanks!

Jeff

j beede wrote:Any chance that the power transformer has recently been re-painted and you are smelling solvents outgassing from partially cured paint?

I believe the transformers are new.  Thanks.

-Jeff

Jeff,
Send me an email to: dynakitparts@aol.com and I will send you back a wiring pictorial of our ST-70. It is slightly different than the original.

Did you buy this amplifier from someone in Texas?

Kevin

if at all possible, please take a nice in focus shot of the underside/inside of the amp, it will give us a much better idea of what we are talking about and may help us in figuring this out.
As Kevin also pointed out, that 1.65V BIAS is too high as well.

MontanaWay wrote:if at all possible, please take a nice in focus shot of the underside/inside of the amp, it will give us a much better idea of what we are talking about and may help us in figuring this out.
As Kevin also pointed out, that 1.65V BIAS is too high as well.

I lowered the bias. I wonder if the tubes were run too hot for a while it might have caused the smell. Here is the best photos I have right now. Thanks for your help!

I cannot see anything obvious wrong from the photo's. As j beede suggested, the power transformer does get quite warm and any new paint, may just give off some odor for a little while.
Tubes too get hot, upwards of 300F and more.
Important thing is get that BIAS voltage down to about 1.00VDC. What output tubes are you running? If they are KT88 or 6550, 1.00VDC is good, if they are EL34, get it down to 0.80VDC per side.
If you still think things are not right, check B+ voltage, should be between 370 and 410 VDC.

MontanaWay wrote:I cannot see anything obvious wrong from the photo's. As j beede suggested, the power transformer does get quite warm and any new paint, may just give off some odor for a little while.
Tubes too get hot, upwards of 300F and more.
Important thing is get that BIAS voltage down to about 1.00VDC. What output tubes are you running? If they are KT88 or 6550, 1.00VDC is good, if they are EL34, get it down to 0.80VDC per side.
If you still think things are not right, check B+ voltage, should be between 370 and 410 VDC.

Thanks so much. I'm currently running EL34 so I will drop the voltage as recommended. Could have been running way too hot!

Cheers

After lowering the bias the smell less smelly, the chassis not as hot & the amp sounds better!  Thanks for all the help!  I think the amp was running too hot causing the issues.  With the SP14 sounds great!

Cheers

Jeff V. wrote:After lowering the bias the smell less smelly, the chassis not as hot & the amp sounds better!  Thanks for all the help!  I think the amp was running too hot causing the issues.  With the SP14 sounds great!

Cheers

thats great news, glad it seems to be all sorted out for you! Enjoy some really nice sounding music.
For future reference, maybe down the track you may wish to consider upgrading to the VTA driver board, I am sure it will sound better again, and, BIAS is split up into all four power tubes, this way, you can adjust the BIAS for each power tube individually, allowing for and 'correcting' any variations in each power tube.
You will need to do some minor re wiring and add 10OHM 2W BIAS resistors to each power tube socket, all this is pretty straight forward and full instructions are available from Tubes4Hifi when you purchase the VTA driver board upgrade.

Jeff V. wrote:After lowering the bias the smell less smelly, the chassis not as hot & the amp sounds better!  Thanks for all the help!  I think the amp was running too hot causing the issues.  With the SP14 sounds great!

Cheers

New oil capacitors will smell too, while they're burning in.

Sometimes items that once got hot, or their neighbors will smell for a while, even though everything is okay. That burning smell seems to get into everything.

deepee99 wrote:

Jeff V. wrote:After lowering the bias the smell less smelly, the chassis not as hot & the amp sounds better!  Thanks for all the help!  I think the amp was running too hot causing the issues.  With the SP14 sounds great!

Cheers

New oil capacitors will smell too, while they're burning in.

Kevin said he believed the parts are a 2005 vintage.  The amp looks brand new so I'm not sure if it was recently built or well taken care of.

nmchiefsfan wrote:
Sometimes items that once got hot, or their neighbors will smell for a while, even though everything is okay.  That burning smell seems to get into everything.  

A possibility.  I know with the tubes being over biased they were ultra-hot.  Still a bit of smell but not as bad.  I need to check the B+ voltage to make sure it's within spec.  Since lowering the bias the chassis is not as hot, but between the El34's it quite hot.  This could be normal.  Thanks.

tubes can and do get hot! Not sure about the EL34, have not run a set for months now, but say KT88's and KT120's, I see temps of 340F when I push them hard, especially the rear ones since they are closer to the transformers.
Average be in the high 200's.

new amp smell, way kind of different than new car smell . . . usually the paint and varnish on the transformers . . . .