L-pad attenuator - smoke

[christien]

I've built an l-pad attenuator to go between my amp and speaker cabinet.  I'm a complete newbie at this (modified my TS9 successfully, but that was my first project), and I only have a basic understanding of this stuff.  Anyway, I hooked it up today, and the l-pad started smoking.  I've read that a bit of smoke when brand new isn't uncommon, but this kept going for over 5 minutes, which seems long to me.  I did have the l-pad cranked so the volume was really low - maybe 1 or 2 notches from silence.

The head is a Traynor YBA (1974, so pre-master-fader) running into a Marshall 4x12 cab.  The amp is (as far as I know) 50 watts (doesn't say anything, just learned that from google - some claim 40w).  It's 8 ohms, as is the cabinet.  I bought a 100w 8-ohm L-pad (Parts express part # 260-262) so the numbers all look proper.

Am I just drawing off too much sound for the l-pad to take?  Would it be fine at higher output volumes?  Or does it take 20 minutes or so to stop smoking?

Thanks for any help with this.

[PRR]

Welcome.

PE does not say so, but that L-pad wants to be mounted on a large metal panel to pull the heat out. It will be very very stressed with 100W in open air.

The numbers on old Traynors were, uh, different. However this is a 40-50 Watt amp "clean" (well, clean-ish) which when SLAMMED will make 70-90 Watts of utterly distorted heat. If the amp was maxed and the speaker was not wall-shattering, most of that heat has to go into the pad.

How hot is it? Hot enough to sizzle spit on your finger? Hot enough to char tissue paper? Hot enough to melt the solder on its terminals? (I've done that, with a transistor, and it worked 20 minutes that way.)

[PRR]

Wait a second. There are several Traynor "YBA".

The YBA-1 was rated by Pete as 90W clean, 150W full sustained power. This is a LOT for a pair of 6CA7; Pete had his own measurement scheme. However it sure could be 70+Watts clean and 130+ Watts of gross distortion.

YBA-2 seems to be the little BassMate which can't hot-up that L-pad.

There is a classic YBA-3; also several later models with YBA in the name.

What do you have? How many what-type power tubes?

[christien]

Thanks for the replies. The l-pad is mounted on a small piece of metal, probably 4x4", maybe 4.5. I was going to mount it in a metal box, but haven't closed it up yet before testing it. The dial gets warm, as does the bottom of the l-pad, but not hot enough to burn anything. It's uncomfortable, but I doubt it's be hot enough to seriously burn my finger if I left it there. The smoke appears coming out where the terminals enter the housing.

I didn't realize the 40-50 watts was at less-than-max output, I always assumed an amp's wattage was its max.

It's not a yba-1, just a yba. I believe the yba-1 was the model that introduced a master volume control.  It's new to me, so not overly familiar with it, and I'm not home so can't check how many tubes or what they are. I can check when I'm home tomorrow night.

[PRR]

Well, maybe there's just too much oil or dust on it.

I believe Parts Express is good about refunds. Beat on it before the return period runs out.

[zombiwoof]

I once tried running a Vibro Champ into a White Bassman head using a 100 watt L-pad, after reading about guys doing this to use the Champ as a preamp of sorts.  Sounded awesome for a couple of minutes then smoked out and I abandoned the idea.  I didn't know about mounting the L-pad on a panel or in a box though.
Al

[christien]

Ok, just got home and had a look. It has 2 Ruby EL34s, 2 Phillips 12AX7s and 1 Electro-Harmonix a 12AX7.

[thehallofshields]

How do these guys work out in practice? Seems like they would have some trouble dissipating the heat.

[smarkalet1]

While researching my Lpad project for my 120 watt head, I saw quite a few people recommending doubling the the assumed wattage ratings when dealing with tube amps. As such I actually got a stereo 100 watt Lpad and wired the speakers in my 2x12 separately. It worked out very well.
If you check the wiring schematic of a 4x12 you will see that two sets of speakers are wired together and then the two sets are wired together in parallel. You can stick a stereo Lpad there if you don't find success worth the part you have. Otherwise try looking for a 200 watt Lpad.
Good luck.

Sent from my LGMS330 using Tapatalk

[wavley]

Wait a second. There are several Traynor "YBA".

The YBA-1 was rated by Pete as 90W clean, 150W full sustained power. This is a LOT for a pair of 6CA7; Pete had his own measurement scheme. However it sure could be 70+Watts clean and 130+ Watts of gross distortion.

YBA-2 seems to be the little BassMate which can't hot-up that L-pad.

There is a classic YBA-3; also several later models with YBA in the name.

What do you have? How many what-type power tubes?

I'm the proud father of several Traynors, I'm a pretty big fan.  Pete tended to rate things as "XX Watts Sine Wave" so they can definitely peak at quite a bit more, leading to the marketing "There are Watts and then there are Traynor Watts"

As Paul just said, I'm guessing that you have the YBA-1, it's two 6CA7s being pushed pretty hard, but if I remember correctly there was a problem with 6CA7s at some point and the later ones are just regular EL34s.

Definitely agree on the YBA-2 assessment, the early ones are two 6V6s and they ended up with EL84s.  I had an YBA-2AB transition model that I bought off the bass player of White Witch for a long time and my old roommate still has it, wouldn't smoke that L pad.

Now, the YBA-3 is four 6CA7 outputs, I don't imagine that L-pad would last very long under that abuse using much attenuation.

I like the way Weber rates they're attenuators "100 watt slight attenuation, 50 watt full attenuation."

There's a pretty defunct Yahoo group for Traynor amps, you can join it and still have access to years of email exchanges about all these amps.  It used to be very active and I miss my daily schooling on amps, those guys knew a lot.  The reason I bring that up is they were pretty big on power scaling as the best way to get more crunch.  Actually, there is a lot of little things you can do to Traynors that improve them but don't fundamentally change their tone.  I still have a 69 YSR-1 in my rig, I have a 72 that I almost use as a tube amp breadboard because the top comes right off and it's so easy to work on, they're just wires, caps, and resistors... I can put it back to stock whenever I want.

I'm not an authority on using an L-pad, I just use smaller amps for less loud and bigger amps for more loud, but I'll certainly help out if you blow that Traynor up

[wavley]

Thanks for the replies. The l-pad is mounted on a small piece of metal, probably 4x4", maybe 4.5. I was going to mount it in a metal box, but haven't closed it up yet before testing it. The dial gets warm, as does the bottom of the l-pad, but not hot enough to burn anything. It's uncomfortable, but I doubt it's be hot enough to seriously burn my finger if I left it there. The smoke appears coming out where the terminals enter the housing.

I didn't realize the 40-50 watts was at less-than-max output, I always assumed an amp's wattage was its max.

It's not a yba-1, just a yba. I believe the yba-1 was the model that introduced a master volume control.  It's new to me, so not overly familiar with it, and I'm not home so can't check how many tubes or what they are. I can check when I'm home tomorrow night.

Missed this part.  YBA-1 is the very first model Traynor, they did not have master volumes... four inputs, two volumes, bass, treble, low range expander (mids), and high range expander (presence)

There's no such thing as just the YBA, but the YBA-1 went through a lot of changes over the years, most of them were cosmetic, but there are some small circuit and power rating changes.

By the way the YBA-3A Super Custom Special was 250 watts and is a pretty rare bird, they made you run two Big B 8x10 cabs to handle the power.

[PRR]

6CA7 is the US tag for EL34. (There used to be some slight difference, but that was long ago and those tubes are all burned-up now.) 6CA7==EL34 for practical purpose. ("EL34" covers several variations of internals.)

All audio amplifiers can make square waves. No music (except overdriven geetar) gets close to square waves. And how would you know if a square was "distorted"? By convention, we test with Sine waves. For the same peak volts, a square makes *twice* the Watts of a roundy Sine wave. Hence the ~~2X adjustment from "low THD" to "cooking eggs instead of ears".

If you *only* want BIG loss, three 8r 100W resistors with the 8r L-pad will quadruple the power rating.

[d95err]

I've had similar problems with a similar L-pad. The L-pad itself could take the heat, but the solder joints and insulation on the cables melted. that was a 30W amp into a 100W L-pad.

You could try adding a fan to reduce the heat. You could even drive it from the speaker signal (see the Marshall Powerbrake).

Or add some fixed power resistors before the L-pad to reduce the power handled by the L-pad.

[christien]

Lots of great stuff here - thanks a lot, I really appreciate it!

wavley, you're right, it is indeed a YBA-1, says so right on the back.  My mistake.  I've sent a request to join that yahoo group - thanks for the tip!

So, if I need a stronger l-pad, is this one any different from the one I bought?  It says 100w RMS, 200 peak:
http://www.ebay.ca/itm/Speaker-L-Pad-Volume-Attenuator-3-8-Shaft-100W-RMS-200W-Peak-8-Ohms-/300916481156

This is the one I have now, says 100w RMS: https://www.parts-express.com/parts-express-speaker-l-pad-attenuator-100w-mono-3-8-shaft-8-ohm--260-262

Or should I just step up to this? https://www.madisoundspeakerstore.com/l-pads-attenuators/fostex-r82b-200w-l-pad/

[d95err]

A note about output levels: 3dB of attenuation is equivalent to half the power. -6dB is quarter power and -9dB is 1/8th of the power. -9dB is woyld still be rxtremely loud for your amp, but the attenuator would be handling 87.5% of the ouput power.

So, attenuating less isn't particularly effective for reducing heat, unless you only attenuate by tiny amounts (e.g. less than 3-4dB). Below that, the attenuator is approximately taking the heat of the full power of the amp.

My solution for playing and recording cranked amps at home is to use a reactive dummy load and a DI-box with speaker simulation (BluGuitar BlueBox) and run the DI signal to my studio monitors or headphones. I get a better tone from that compared to trying to attenuate the amp output. For stage and rehershal levels, an attenuator works OK.

[christien]

Yeah, this is for stage, not for home practice.  So tone is pretty crucial, and I still need a decent amount of level.

[wavley]

6CA7 is the US tag for EL34. (There used to be some slight difference, but that was long ago and those tubes are all burned-up now.) 6CA7==EL34 for practical purpose. ("EL34" covers several variations of internals.)

All audio amplifiers can make square waves. No music (except overdriven geetar) gets close to square waves. And how would you know if a square was "distorted"? By convention, we test with Sine waves. For the same peak volts, a square makes *twice* the Watts of a roundy Sine wave. Hence the ~~2X adjustment from "low THD" to "cooking eggs instead of ears".

If you *only* want BIG loss, three 8r 100W resistors with the 8r L-pad will quadruple the power rating.

Paul is correct, for all intents and purposes 6CA7s and EL34s are the same tube in a circuit, the 6CA7 Pete originally used is a beam tetrode (like a 6L6) tube and has a moderately different negative bias requirement that's close enough for rock and roll to be interchangeable with EL34 pentodes... quoth Paul "("EL34" covers several variations of internals.)"

The only reason I brought it up before is that Pete was running original 6CA7s in a circuit that would eat an EL34 at the time when Philips changed their process to what make them identical to an EL34 without telling him and his amps started failing so they had to massage the circuit to be nice to pentode 34s which explains the variation in output powers of the same amp models with the same "6CA7" output section.  (Similar things like this happen all the time, like how I found that Acoustic amps run 2n3055s at 85 volts, modern ones can only handle 60... instant meltdown, turns out old ones could handle 100 volts)

These days you can choose between pentodes or beam tetrodes to put in a 6CA7/EL34 circuit, they have some not earth shattering sonic differences, but differences nonetheless.  I like the JJ 6CA7 in my Traynors, to my ear they sound right in these amps for my taste.  The thing I like about Traynors is that they're pretty Canadian... a little bit U.S., a little bit U.K., and all rock and roll.

[thermionix]

The thing I like about Traynors is that they're pretty Canadian... a little bit U.S., a little bit U.K., and all rock and roll.

Heck yeah.  Most circuits are either Twin Reverb based or Marshall plexi based.  I have one of the latter in for a cap job right now.  Their wiring was a little bit sloppy but good enough.  Those old Hammond transformers sound great and are damn near bulletproof.

[wavley]

The thing I like about Traynors is that they're pretty Canadian... a little bit U.S., a little bit U.K., and all rock and roll.

Heck yeah.  Most circuits are either Twin Reverb based or Marshall plexi based.  I have one of the latter in for a cap job right now.  Their wiring was a little bit sloppy but good enough.  Those old Hammond transformers sound great and are damn near bulletproof.

There's a few Traynor fans around here, Aron being one of them. 

Hammond still makes pretty much the same transformers.  My first one has a replacement output transformer, it's the reason I learned to work on electronics... I dropped it off at a shop to be recapped and finally got it back 8 months later and he had somehow cooked the output tranny (traynors have a resistor to help keep this from happening, I don't know how he did it), and held it hostage for $238.  I decided that no one would ever touch my stuff again, read up on amps, ordered a transformer, put it in.  It worked great for a while, then it started motorboating... turns out that the only caps he changed were the cathode bypass caps!  The solders on the can caps had never been touched. I sound bitter, but now I kinda thank him for starting what is so far a 20ish year career in electronics that I for a while worked at a shop that was in direct competition with my "nemesis". 

[thermionix]

Jeez, what a clown!

I've never seen a Traynor lose a transformer, but it's not like I've worked on hundreds of them.  They're not all that common around here.

Off the top of my head, I don't know what resistor you're referring to that protects the OT.  Can you elaborate?