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Bogen 6-watt matching OT - w/6BQ5?

9/14/1998 3:00 PM
Craig	Bogen 6-watt matching OT - w/6BQ5? I have been trying to figure out a problem with my single-ended DIY amp. Tube complement: Rect.=6X4/Power=6BQ5/Reverb=12AT7/Preamp=12AX7. Near as I can tell, the problem seems to be with the OT, a salvaged Bogen 'T5C', which has the following markings: on top, it has what I assume are impedence references - Common/500/1000/1500/2000. Each has a corresponding lug, so I assume this is the secondary winding, and that this setup allows a choice of primary impedence. The other side of the Bogen (bottom) had 2 leads, green and black, which further confuses me, because these are the colors often used on the secondary. On one side, it says: use above impedences for 8-ohm, divide in 2 for 4-ohm, and multiply by 2 for 16-ohm. I have been running it into an 8-ohm load - a 25-watt, 12" Jensen C12Q. On the opposite side, it says 6 watts, T5C, Speaker Matching Transformer. I need to figure out if this is/isn't an appropriate OT to use with the 6BQ5, and/or the 25 watt speaker. I have an RCA tube manual, but I'm not clear on what to reference. Have I got this thing wired-up wrong? The current situation is that signal is getting amplified, no matter which lug I solder my hot speaker lead to, but it is very quiet, and very distorted. I verified that I am getting reasonable voltages on the 6BQ5: pin 7 - 263v, pin 9 - 250v, pin 3 - 7.4v. I am wondering about the possible effects of tying the Grid 3 (pin 1) to the cathode. I understand Hi-Watt and some others do this, and Kevin O'Conner recommends it for both EL34's and EL84's. Anyone have any idea how to tell what's happening here?

9/14/1998 3:00 PM

Craig

Bogen 6-watt matching OT - w/6BQ5?

I have been trying to figure out a problem with my single-ended DIY amp. Tube complement: Rect.=6X4/Power=6BQ5/Reverb=12AT7/Preamp=12AX7.

Near as I can tell, the problem seems to be with the OT, a salvaged Bogen 'T5C', which has the following markings: on top, it has what I assume are impedence references - Common/500/1000/1500/2000. Each has a corresponding lug, so I assume this is the secondary winding, and that this setup allows a choice of primary impedence. The other side of the Bogen (bottom) had 2 leads, green and black, which further confuses me, because these are the colors often used on the secondary. On one side, it says: use above impedences for 8-ohm, divide in 2 for 4-ohm, and multiply by 2 for 16-ohm. I have been running it into an 8-ohm load - a 25-watt, 12" Jensen C12Q. On the opposite side, it says 6 watts, T5C, Speaker Matching Transformer. I need to figure out if this is/isn't an appropriate OT to use with the 6BQ5, and/or the 25 watt speaker. I have an RCA tube manual, but I'm not clear on what to reference.

Have I got this thing wired-up wrong?

The current situation is that signal is getting amplified, no matter which lug I solder my hot speaker lead to, but it is very quiet, and very distorted. I verified that I am getting reasonable voltages on the 6BQ5: pin 7 - 263v, pin 9 - 250v, pin 3 - 7.4v. I am wondering about the possible effects of tying the Grid 3 (pin 1) to the cathode. I understand Hi-Watt and some others do this, and Kevin O'Conner recommends it for both EL34's and EL84's.

Anyone have any idea how to tell what's happening here?

Replies:

Whit Craig, I think you got it ... -- 9/14/1998 5:15 PM