6v6s into light load

[Doug H]

I've been working on a friends old lifco amp, it's a non reverb Princeton into cathode bias pair of 5v5s. Basically a 5e3 with a tone stack. It used to have just the reverb bridge of the reverb model, but I yanked that whole gain stage out for now.

o after ferreting out a bad rectifier tube it sounds pretty solid in my basement. This amp didn't seem to like pedals that well, I added a series grid resistor into the PI and that tightened it up, that and yanking the extra gain stage.

So my buddy plugs in his 40hm 2x10 at an open mic and all the bottom end disappears, some volume too IMO.

This thing has about 295 on the plates and I'm pretty sure the tranny is 7.2k with a 8ohm load. So the cab is definitely stressing the amp, and it's not like Princetons are known for their smooth overdriven tones in the first place. But it sounded bad asssed in my basement into a 1x15, on stage into the 2x10 I couldn't get a meaty tone out of it. I'm gonna drag my 15 out, but I'm wondering, could running a 3.6k load cause this much grief for a pair of 6v6s?

[Leo_Gnardo]

but I'm wondering, could running a 3.6k load cause this much grief for a pair of 6v6s?

Yes you'll lose some power by not running an optimum load, but I'm also suspecting your friend's 10's are wired reverse-polarity to each other. That will take the tone out of anything. Trace the wiring or even faster, do the battery-pop test while watching the cones and I'll bet ya half a peach that's the case.

[Doug H]

there's a thought, I'll be looking into that for sure

[Enzo]

Or the 2x10 cab is wired out of phase.

[Doug H]

I cooled off the bias a bit and added a 470k swap resistor into the PI and it's holds up now under fire without ratting out. I checked the cab and it looked fine and looks like it is still factory wired. Amp sounds sweet now even into his 4 hm cab. We might ultimately swap out the OT but for now it's working. Tubes were just being overwoked it would seem.

Thanks.

[Doug H]

Another question for the same amp. I'm picking up a new tranny from hammond to properly match up with the cab.

To "recap", this thing has about 300v, maybe 310v on the plates, cathode biased 6v6s, cathodyne PI. there are two trannies I see that will work, the princeton r the blues junior.

The princeton has 8k prmiaries, the jr, 6.95. I'm wondering which will give the most volume from a punchy hearoom perspective? I'm leaning towards the 8k, thinking that if the 7k is actually louder, it's stil not gonna have much in the way of clean punch over the 8k. Digging around suggests the lower primary might put out less power, but I haven't found an example of this power stage at this voltage and I can't get my head around those load line charts.

Any thoughts?

Thanks

[Chuck H]

I actually think the 7k would have more power and punch. I think the 8k would make for lower THD and speaker reactance. The difference would be virtually inaudible. I'd go with the 8k only because I seem to prefer the tone of higher impedances when I've used them.

I don't know which Hammonds your looking at but a favorite of mine is the "off the shelf" model 1608. It's rated at 10 watts but you can ignore that. I've used several in 15 to 20 watt amps, many of which live cranked up and the OT is the LAST thing I worry about. Never had a failure. Even with boo boo's like forgetting to plug in a load for a moment while blanging on the guitar! Big bottom and consistent performance. A previous member here used them in his 18 watt builds and won some kind of tone award at an amp show. Sorry for the lack of details. It was probably fifteen years ago.

The "guitar amp replacement" OT's are probably less expensive and I hear good things though I've never used one.

EDIT: One more note. I built a design for a guy in 2008. The prototype used a Hammond 1608. The production model protos used custom Heyboer units. That prototype is now my personal amp, and my favorite. I also have one of the production protos They both sound great. The one with the 1608 gets the nod though.

[Doug H]

The hi fi ones do seem to cost a bit more, that puts them off the short list for this particular project, but thanks for the heads up. I've got one of their 125 (i think) universal 10 ir 15 watters in a pp 6aq5 amp, works great.

I'm leaning towards the 8k myself, and it's for a high gain player as well.

[Alan0354]

The "guitar amp replacement" OT's are probably less expensive and I hear good things though I've never used one.

Do you have a link for this?

[Chuck H]

We were discussing Hammond products. Most amp part distributors carry some or offer all of the Hammond guitar amp replacement transformers. So rather than link I'll let you do the searching since prices will vary.

[eschertron]

Chuck, are you saying that you don't use *any* off-the-shelf guitar OTs, or just haven't used any by Hammond?

[Alan0354]

We were discussing Hammond products. Most amp part distributors carry some or offer all of the Hammond guitar amp replacement transformers. So rather than link I'll let you do the searching since prices will vary.

I thought "Guitar Amp Replacement" is a brand of OT!!! I like to try some cheaper transformers rather than going to expensive ones. I tried one OT from Magnetic Components.....more specific, the OT for Bandmaster/Vibrolux/Pro Reverb. I heard Fender used Their transformer in their older amps. Is that true? I notice the size of the OT I bought is very close to the size of the Fender Pro Reverb also.

I notice better quality transformers or speakers tends to have more lows and highs. When I tested out better speakers like Celection in my Pro Reverb, it has too much bass and highs. It's like Fender design the amp around the cheap Utah speaker and I really like the sound of the original speaker with the amp.

I am trying to design the amp that can sound good with cheap components rather than starting with expensive components.

[Chuck H]

I thought "Guitar Amp Replacement" is a brand of OT!!! I like to try some cheaper transformers rather than going to expensive ones. I tried one OT from Magnetic Components.....more specific, the OT for Bandmaster/Vibrolux/Pro Reverb. I heard Fender used Their transformer in their older amps. Is that true? I notice the size of the OT I bought is very close to the size of the Fender Pro Reverb also.

I notice better quality transformers or speakers tends to have more lows and highs. When I tested out better speakers like Celection in my Pro Reverb, it has too much bass and highs. It's like Fender design the amp around the cheap Utah speaker and I really like the sound of the original speaker with the amp.

I am trying to design the amp that can sound good with cheap components rather than starting with expensive components.

That shouldn't be a problem. But remember that while less expensive parts CAN make for a good sounding amp it won't be the sort of amp that you would make from more expensive parts What I'm saying is that WRT guitar amps there are some that sound good because of the deficiency of their components and some that sound good because of the excellence of their components. They are different amps with different sounds.

[JoeM]

......
I am trying to design the amp that can sound good with cheap components rather than starting with expensive components.

Personally, components I would not go "cheap" are transformers and speaker(s). Resistors, caps, not so much. Good pots are nice too. Why build an amp with cheap components that sooner or later you would want to upgrade?

[Alan0354]

That shouldn't be a problem. But remember that while less expensive parts CAN make for a good sounding amp it won't be the sort of amp that you would make from more expensive parts What I'm saying is that WRT guitar amps there are some that sound good because of the deficiency of their components and some that sound good because of the excellence of their components. They are different amps with different sounds.

Ha ha, I am born cheap!!!! I take it as a challenge to make cheap component sounds great!!! Fender make do with cheap transformer and el cheapo Utah speaker and make the sound comes alive with my Pro Reverb, so it can be done. I truly do not like the sound of the Celection speaker installed in the Pro Reverb as it's too hifi, so are the JBL. The magic is the whole amp and it's magic. I never thought I would like the old stock Pro Reverb that much. It just have the "biggness" and transparency that stands out. AND everything inside is cheap. Putting the expensive Celection just destroy the magic in my opinion.

That's the reason I start with the Magnetic Component OT and I am looking for a Chinese PT. I am still looking for a cheap speaker. So far the cheapest I found is the Weber model that is $42. If you have some that is mid heavy like the cheap Utah speaker back in the days new, please give me the name.

I know a lot of you disagree with this, but this is what I am trying......or die trying!!!!

Thanks