Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: torren61 on July 11, 2015, 06:43:32 pm

Title: 1968 Traynor YBA-1 Bass Master Voltage Issue
Post by: torren61 on July 11, 2015, 06:43:32 pm

The title is a mouthful.  I recently rebuilt/modded a Traynor YBA-1 head.  It sounds great but my voltages are kinda high.  I'm getting 531 VDC across pin 3 with 123 VAC.  It should be 440 VDC + or - 20%.  That makes the maximum voltage 528 VDC.  I can drop the AC voltage to 95 and it gets me the correct DC voltages but what does that do to my tubes?  Is the heater getting the correct voltage?

Title: Re: 1968 Traynor YBA-1 Bass Master Voltage Issue
Post by: sluckey on July 11, 2015, 09:36:48 pm

Quote

I'm getting 531 VDC across pin 3 with 123 VAC.  It should be 440 VDC + or - 20%.

Are the tubes plugged in when you get that 531v reading?

Title: Re: 1968 Traynor YBA-1 Bass Master Voltage Issue
Post by: torren61 on July 12, 2015, 09:01:37 am

Yes.  Pin 3 reads 531, Pin 4 reads 499, Pin 5 reads 45 on one tube and 44 on the other. I installed a 1 Meg resistor between Pin 1 and ground and it reads .033 on one tube and .038 on the other.

Title: Re: 1968 Traynor YBA-1 Bass Master Voltage Issue
Post by: torren61 on July 12, 2015, 10:32:08 am

I'm running KT77 tubes.  Rated for 800V max.

Title: Re: 1968 Traynor YBA-1 Bass Master Voltage Issue
Post by: sluckey on July 12, 2015, 10:57:06 am

I see several schematics for the YBA-1. Many of them show 537V on the plates. I would not worry. Even with your 531V and 38mA current that's only 20 watts.

Title: Re: 1968 Traynor YBA-1 Bass Master Voltage Issue
Post by: torren61 on July 12, 2015, 11:16:56 am

Could I trouble you to post some of those?  Mine is a 1968 model with a choke and diodes.

Title: Re: 1968 Traynor YBA-1 Bass Master Voltage Issue
Post by: torren61 on July 12, 2015, 11:26:28 am

Here's what her guts look like after my mods:

(http://i.imgur.com/9y649ZFl.jpg)

Title: Re: 1968 Traynor YBA-1 Bass Master Voltage Issue
Post by: sluckey on July 12, 2015, 11:55:23 am

Quote from: torren61 on July 12, 2015, 11:16:56 am

Could I trouble you to post some of those?  Mine is a 1968 model with a choke and diodes.

Just follow the link for "Tube Amp Schematics library" at the bottom of this page.