Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pbman1953 on June 18, 2011, 08:51:32 pm

Title: How to Bias Traynor YBA-3A Super Cust. SP
Post by: pbman1953 on June 18, 2011, 08:51:32 pm

I used to know how but I forgot. Guy and Clarence , over the phone from Traynor told me how. I just forget


There's a red wire coming off the power transformer that gets removed and a multi meter interupts the connection. then you measure 100ma, with no signal. I can' t seem to get the measurmemt. Possibly someone ones knows and remembers. It is real simple

Here's the schematic-

http://www.0rigami.com/vb/traynor_customspecial_yba3a.pdf (http://www.0rigami.com/vb/traynor_customspecial_yba3a.pdf)

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: sluckey on June 18, 2011, 09:09:25 pm

According to the info on the schematic...

Disconnect the red wire (primary center tap) of the OUTPUT TRANSFORMER. Connect a milliamp meter between the red wire and where it was connected. Negative meter lead connects to the red wire.  Adjust for 100ma.

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: pbman1953 on June 18, 2011, 09:13:18 pm

On what scale of the meter. That's the part I forget

Thanks

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: sluckey on June 18, 2011, 09:23:42 pm

set meter to measure milliamps. some scale greater than 100ma.

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: pbman1953 on June 18, 2011, 09:45:33 pm

dc or ac

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: LooseChange on June 18, 2011, 11:00:19 pm

Dc and please be careful... Thats a lot of voltage!

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: pbman1953 on June 19, 2011, 06:37:41 am

My meter has a "MA" setting and an AC & DC toggle button The setting is AC. Th funny thing is that I was getting no reading and a buzz. Using a plastic probe , I touched some of the components to try and isolate the buzz. I found a broken chassis ground at the connection for the  of the 2- 200 uf caps on the diode stack. I ran that lug to a ground and the buzz is gone and the reading came back

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: pbman1953 on June 22, 2011, 07:53:58 am

After the repairs everything was running. After a bit , the amp loss power and started to hum. The notes buzzed through the amp.After the night was over I looked inside and did a little probling with my plastic probe. The 2 larger filter caps I installed would be intermittent when I unclipped them and moved them around. One position fine , another buzz. Please understand that this amp goes nowhere, no travel. All the filter caps were changed last year. I'm thinking that the one cap may have an intermitent connecttion internally.


Has anyone run into that? Is it possible to remove the caps and still run the amp?

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: sluckey on June 22, 2011, 08:32:29 am

Are you talking about C27 and C28? Those caps are essential to the operation of the amp.

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: pbman1953 on June 22, 2011, 08:37:51 am

Yes, I replaced the silver can cap with 2-  220 uf's @ 350 v-
in series-  also using 2- 100K res.

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: pbman1953 on June 22, 2011, 01:05:17 pm

Also, I happen to have a spare 100 uf @ 450v. Is there any advantage to upgrade the 40 uf @ 450V to that one?

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: sluckey on June 22, 2011, 10:07:32 pm

Quote from: pbman1953 on June 22, 2011, 01:05:17 pm

Also, I happen to have a spare 100 uf @ 450v. Is there any advantage to upgrade the 40 uf @ 450V to that one?

I don't think so.

Title: Re: How to Bias Traynor YBA-3A Super Cust. SP
Post by: pbman1953 on June 23, 2011, 06:01:08 am

Even the cap 40 uf cap that replaced the can cap?