Thunderbird Club

[Chucky Stiletti]

Cathode bias isn't necessarily class A. And if they're truly getting 15W from the amp, they'd really be pushing it with class A. Well, depending on the tube brand. Did you measure voltages and current in the output stage?

I designed a clean 7W single EL84 amp; I spent hours and hours testing tubes. I forget now what I settled on, but there were only 2 or 3 brands that would handle the abuse and sound good. I was working on ways to switch between a baby Twin clean sound and a more Kalamazoo Model One dirt but never came up with anything I was happy with. I did mate an Orange preamp with both a VOX AC-15 output stage and a Fender Deluxe output stage. Loved both of those.

it's class A, based on Dick Denny's Vox AC15 design....don't need to measure currents or Voltages if I have the amp power spec, schematic and tube datasheet...

 

[Chucky Stiletti]

It has been a while since I have analyzed such things, but the configuration of the output transformer look to me like a push pull arrangement, not class A. Then again, the second gain stage does not look like it is inverting the signal. Colour me confused.

As far as running at 4 Ohms, unless there is a 4 ohm tap, I am unlikely to do it. What I can't understand is that output transformers with a 4 ohm tap are commercially available and do not meaningfully change the BoM cost.

because you are thinking of single ended amplifiers. Class A can be accomplished with push pull and this aids in even order harmonic cancellation..

 

[Miles_ONeal]

I've listened well over 100 times to the 1972/08/27 (Venetta, OR) version of "I Know You Rider" I posted last week, absorbing the bass line (or playing along with it). The only problem is that I now think the song ends with the rap about "my friend Durango" and a water report.

It's been way too long since I did this with a song!

 

[Chucky Stiletti]

Is it a common problem, or are they just random JDs?

to hit the price range, these have to be PCB based....unfortunately FR4 and heat don't get along well..

 

[Miles_ONeal]

it's class A, based on Dick Denny's Vox AC15 design....don't need to measure currents or Voltages if I have the amp power spec, schematic and tube datasheet...

I always check for myself. Don't trust mfrs to provide 100% accurate info. Learned that early on.

 

[Chucky Stiletti]

I always check for myself. Don't trust mfrs to provide 100% accurate info. Learned that early on.

I first measure the output power and use that as a benchmark.
what method do you use to measure OT Ip?

 

[Chucky Stiletti]

I'm not. I know push-pull guitar amps can be class A or AB. But the method of bias and the class are not synonymous. Again, I just don't trust mfrs; there's too much BS. I worked on a number of amps that were billed as class A just because they were cathode biased- but weren't. I generally assumed that was just marketeers taking over. Maybe Orange gets it right. But they'd be in the minority.

I was responding to PillO..

 

[Miles_ONeal]

You can do 15W Class A by running 2 EL34s parallel. Push pull can be done too, but requires a different O/T configuration. Amps such as the SVT run push pull with 3 6L6 parallel on either side of the phases.

This was specifically in relation to the dual EL84 config such as the Tiny Terror uses. 8^)

 

[PillO]

I'm not. I know push-pull guitar amps can be class A or AB. But the method of bias and the class are not synonymous. Again, I just don't trust mfrs; there's too much BS. I worked on a number of amps that were billed as class A just because they were cathode biased- but weren't. I generally assumed that was just marketeers taking over. Maybe Orange gets it right. But they'd be in the minority.

The reply was aimed at me because I was confused by the lack of an inverter and the 3 input taps to the O/T

 

[Miles_ONeal]

I was responding to PillO..

Yeah, just realized. Sorry.

 

[PillO]

Yeah, just realized. Sorry.

You can be as confused @JJR58 some of the time, or you can be not as confused as @JJR58 all of the time, but you can't be as confused as @JJR58 all of the time.*

*with apologies to PT Barnum and @JJR58

 

[Miles_ONeal]

I first measure the output power and use that as a benchmark.
what method do you use to measure OT Ip?

Initially I measured Vp and the OT DCR and compute it, but I later used an inline ammeter.

 

[Miles_ONeal]

You can be as confused @JJR58 some of the time, or you can be not as confused as @JJR58 all of the time, but you can't be as confused as @JJR58 all of the time.*

*with apologies to PT Barnum and @JJR58

(picks up gauntlet and smirks)

 

[Chucky Stiletti]

Initially I measured Vp and the OT DCR and compute it, but I later used an inline ammeter.

an ammeter with the bandwidth of an audio test signal?...hmmm...what kind was it?

 

[Miles_ONeal]

When I was building, I also got the impedance from my tranny provider, measured the output voltages, and went from there.

 

[Miles_ONeal]

an ammeter with the bandwidth of an audio test signal?...hmmm...what kind was it?

I wish. I thought you were talking about DC on the plate. For AC I'd get as close on the output side as I could and work backwards based on the OT ratio.

 

[JJR58]

You can be as confused @JJR58 some of the time, or you can be not as confused as @JJR58 all of the time, but you can't be as confused as @JJR58 all of the time.*

*with apologies to PT Barnum and @JJR58

an amateur.

An amateur confused?

 

[JJR58]

When I was building, I also got the impedance from my tranny provider, measured the output voltages, and went from there.

Tranny provider? what's going on around here?

 

[BklynKen]

I have liked this post also. I suppose until @BklynKen starts looking at his likes, we will have to post to let him know we "liked" his post.

As you like.

 

[PillO]

Is it still Thunderbird Thursday?