My Shuguang 274B arrived yesterday and is not only beautiful to look at (just cool…seriously), it works really well. I've bought some Psvane and other Chinese tubes over the years and have been somewhat disappointed with the fit and finish (some, not all) and have had a couple simply fail…but this 274B seems really well made and, of course, hasn't failed yet (almost a day in service).

I was moving my kt88 Fire-Bottle when I heard something rattling inside, so I took the back off.

It was a rubber sleeve that wrapped around a resistor near the PSU. The heat literally baked it off, it was hard and rattling in the case.
Resistor pictured: https://c1.staticflickr.com/5/4299/3...662e931d_b.jpg
It's the one that says XICON.

I also noticed while I was looking in there that similar resistors near the back melted the coating off some other resistors, pictured: https://c1.staticflickr.com/5/4297/3...82acbedb_b.jpg
I hand parted those four resistors apart as far as the wire would let me. They were originally smashed together with no space. I also drilled holes on the underneath cover. Three holes under the PSU, and four under those four resistors.
Now when I have it on, I can squeeze my hand underneath the Fire-Bottle and feel 100F+ heat billow out of the amp :thumbsup:

I always knew the thing got hot, but I assumed Dennis knew best as far as heat effects. I mean a metal box with no vents is a torture chamber for electrical parts.
I know the holes in the bottom cover might reduce resale, and some might think it ugly, but a steel box with no vents is no bueno in my book. Just thought I'd pass the info along.

Inspected mine right away. As I have the 17wpc version, I was concerned that there would be even more heat buildup. Plus I run less efficient speakers and thus probably at higher output wattages. But no sign of any damage in mine. My circuit layout looks different than yours. Does yours have the 20W output transformers? Perhaps those run a bit cooler, as they are larger, than the 15W ones?

That's concerning! I will check mine and maybe cut a replacement bottom from hardware mesh (home depot/lowe's) to allow ventilation while preserving the original bottom plate even if no evidence of heat damage - just to be safe.

http://i.imgur.com/mAnN3hn.jpg

You may remember I cooked a couple resistors with my PSE a while back because I was running tubes (6K6s) which were not compatible with the voltage of the circuit. When inquiring with DH I learned the rubber sleeves on the resistors are for secrecy. Heat shrink to hide the values from copycat eyes. Anyway, I would contact DH about this. If this lack of ventilation was a design flaw others would have had the same issue. I have a feeling something is out of whack. It may have been a tube going nuclear that intern caused a Cap to vary with use and then cause further heat due to varying voltages and to much current draw. I guess what I am saying is that the holes may help with a symptom but not solve the root cause.

I was using kt66 pair with 6sn7 and 5u4g rectifier, all standard Dennis recommended tubes.

And on mine, with no damage, I have been really pushing it. Running KT120 with GZ34 rectifier for maximum output. I do have a bit of a larger chassis than the standard KT88 HO. So more space and components are not as crammed together. I cannot ever remember my chassis feeling hot, or even moderately warm.

Yep, those are a fine selection of tubes. IMHO though something is a miss besides vent holes causing things to run to hot and burn up passives. My KT amp runs cool cool. Chassis is a touch above room temp and PSs are slightly warm regardless (mid 80's F) of the tube combos. I renew my suggestion to contact DH and get his take.

My chassis is 14.25" x 7.5" I've been under the impression that this is a bit larger than the standard. But don't really know.

I received this from Dennis to pass on to allay concerns:

My chassis is the same size. The amp runs hot with KT88's etc.

The heat really can't escape from my HO, but since it hasn't melted I'm OK with it (I'll look inside for shrink wrap issues). Also, I'm a little confused as to which rectifier to run with KT77s…my options are a 274B, GZ34, and the supplied 5Y3S. I'm leaning toward the 274B from what I've gleaned from these posts, but advice is welcome.

I've tried many rectifiers, to name a few:

JJ GZ34, J 5U4G, RCA NOS 5v4g, JAN-Sylvania 5Y3WGTA, Mullard f31 fat base gz34, Preferred Series 274b, Bendix 6106 (5Y3 Variant), Sophia Electric 274b mesh, Psvane 274b treasure mkii, Sylvania 5931 (5U4WG sub), GE NOS 5R4GYA, Philco Sylvania 5U4G Hanging Filament, RCA 5R4GY hanging filaments single bottom getter, PHILIPS 5R4GYS (made in holland), NOS 596 (sub for 274A 5U4G 5R4), 1940s RCA Jan Crc 5R4GY hanging filaments double bottom getter

My favorite overall is the 596 rectifier (has same specs as 5u4g).
GZ34 boost low end in my experience, but decrement detail(resolution). I'd actually say the GZ34 I've tried are my least favorite type, and to extend that the GL gz34 severely decreases detail, sparkle, and air. (YMMV IMO)

Princess 274b is decent, but middle of the pack for me. I like 5u4 and 5r4 the best. There are ideal pairing I have that take into consideration the input and output tubes I'm using. In that vain what works best for the kt77 I'm not sure, it's one of the few output tubes I don't own.

I think gz34 has potential for me, but I'm not willing to spend $300+ on a metal base version from Mullard. The F31 fat base was superior to the GL for sure, at least for me, but still those are expensive.

I've found since gz34 are hyper common/popular, it's insanely hard to find good NOS variants for cheap, while 5u4 and 5r4 are easy to find the "holy grail" versions for a bargain if you look long enough.

To cap off, I think the 274b might be your best bet for detail, gz34 if you need low end, 5y3 idk. I own a few 5y3 including the Bendix, but I've never loved them like my 596.


p.s. @pstrisik

Thanks for the info. In that sense there's probably nothing wrong with my fire-bottle, and no reason for concern or vent mods.
The rubber baking off now makes sense, and the two resistors in the back probably only started melting for two reasons, #1 they were smashed against the resistors, #2 even tho the caps are rated for high degrees, the covering and adhesive the "hifi" brand used on them is probably cheap and came unglued from prolonged heat.

One last thing: I've read the U52 rectifier is exceptional, but again one of those holy grail tubes, I can't find one for under $400 myself. If I ever see one <$200 I'd snap it up.

I have a fair number, but not as many, rectifiers too. Maybe 15-17 or so. But my experience in hearing differences between them is much different than Comzee's. Within a rectifier type, I hear no differences between them. I can hear differences between 6SN7s, sometimes fairly significant differences. I hear differences between 6SN7 vs 6SL7 tubes. But between about 10 5U4GB & 274B rectifiers, they all sound the same to me. Switching between GZ34 to 274B to 5V4, I hear small differences.

A friend loaned me an expensive Psvane 274B and I compared it to my 1950s vintage Motorola 5U4GB and a Tubestore Preferred 274B (which Dennis supplied with my amp). I couldn't detect the slightest difference in sound.

The inexpensive JJ GZ34, which also came with my amp, is fine too.

I basically try to match my rectifier to my output tubes in order to maximize the strengths of each output tube type. Using my 5V4GAs with 6V6s, 5U4GB/274B with most output tubes, and GZ34 with KT88/KT120 (and occasionally KT66). As to which 5U4GB/274B or GZ34 I use, I pick the one which I think looks best with a specific output tube. Or if I'm feeling sorry for a particular rectifier tube which hasn't been used in a long time. ;)

I am not alone in this opinion. When this has been discussed on the Audiokarma board, most people will say that they hear no differences. A few will claim that they do.

I would run a 274B or 5U4G/GB with KT77s. Well, that is what I actually do when I'm using KT77s. This would push another watt or two out of them, as compared to using a 5Y3S. But that doesn't mean you would like this combination better. In your system and using your music, you might prefer the KT77s running a little more relaxed. Given that you can pick up 274B/5U4G tubes for $10-$25, I'd grab one and run a comparison.

I've heard differences among the little collection I now have, and as long as the Shuguang 274B continues to sound OK it gets to stay due to its general crazy look, and I'll try it with the 77s.

Try them all but I think you will prefer the 274B.

This in today from Dennis. Can't wait to hear it.
Attachment 51381

Tell us more BC. :scratch2:

Well this is my 2013 vintage KT66/88/120 which I had Dennis do the IIPS to. Different than others, this chassis is as big as the PSE so there is a lot of space in there. Instead of transitioning to ss rectification which he typically does He had Straitwire drill a hole for a second rectifier tube. The rear right is still acting as a ac-dc rectifier. The front right direct heated rectifier tube is the IIPS "nasties" blocker. I can tell this pict shows its 'just wired' state. It is sitting directly on the table. No bottom plate and feet. Anticipation is killing me.

Those are solen film caps that are looking a bit fried there, not resistors.

I'm glad you're such a die hard convert. Best kept, inexpensive secret to improved performance.

Interested in the FMOD filters but I have a question. If my sub's highest crossover is 90Hz, would I still use a 100Hz crossover and not use the sub's internal crossover? FYIW my mains have a specified frequency response 38Hz-25kHz, ±3dB with a 5kHz crossover.

I'm sure x3workshop will provide a more informed reply. To me, this is just common sense. We all know floorstanding loudspeaker design is a tradeoff / compromise across such a wide frequency range. Nothing depicts the lowest 100 Hz better than a good, purposely-designed SUB.

Now, instead of reinforcing those low frequencies with the SUB, the filters allow a seamless, continuous bass line across both camps (under and above 100 Hz). The added benefit with the approach is the relief on the flea-powered amp of those nasty last 100 Hz. The end result is better bass, mid-range and highs.

To answer your specific question, you can either use a lower std high-pass filter at 50Hz or you can use the std 100 Hz filter and lose representation of frequencies: 91, ... ,100Hz. Both approaches are improvements, as those last 50 of the 100 Hz range are the most difficult. Your choice. I would personally sacrifice those 10 upper Hz and improve the rest. Maybe this supplier can accommodate a custom 90 Hz High Filter?

Originally Posted by x3workshop: "I'm glad you're such a die hard convert. Best kept, inexpensive secret to improved performance". Trying to keep learning :)

I think a 70hz High pass filter would work just as well for your setup. Perhaps even better.

One thing I will mention about 'Harrison Labs' the manufacturer and vendor of FMods. He seems to have become rather outspoken regarding his religious and political views and has used his website as a pulpit. Be prepared.

Thanks

So what you are saying, is use 70Hz high pass FMOD at the Inspire amp input, correct?

What crossover point on my sub would you recommend? Since I do have a decibel meter, should I play with the sub crossover points and adjust as needed for the best seamless transition?

I did not know there was a std 70 Hz High Pass Filter on offer. Evidently, that is the best approach. Just dial your SUB crossover at 70 Hz to get a seamless bass line. It is mathematical, because the filters make sure the amp does not work under 70 Hz. To avoid reinforced bass, just cross the SUB at 70 Hz. Yes, those filters go at the end of your amp's input cables (R + L) and connect directly to the amp, as usual.

What MA said! Should work very well and you can tweak your sub's xover so that there is no bump.

Thanks for the input, ordered a set of 70Hz high pass filters

I'm going to throw an odd scenario at you guys, and see if anybody thinks they know what it is.

I sometimes use my fire-bottle for headphones. I rarely do though because there's a decently loud hum in the right channel (something you can't hear with speakers).

I recently moved, and I noticed something peculiar. When the furnace kicks on (same house circuit) the hum goes dead silent. That's pretty cool in my book, since the fire-bottle kicks the ass of my normal headphones amps.

Anyway, I'm not sure what the extra load on the house circuit is doing to the electrical properties coming out of the other outlets (of which my fire-bottle is connected). I'm wondering if I can replicate those properties without the furnace being on, to reduce hum to zero?

I would argue the furnace is really well-grounded and so when at work all that circuit's parasitic currents go to ground, relieving the amp from those nasties while that happens. Try to use a dedicated circuit for your audio and make sure it is efficiently grounded. I may be wrong, so better ask an expert.

That sounds correct, from my general troubleshooting.
I'm been thinking of buying a Topaz isolation transformer, not quite sure that would fix the problem though.

I've been using a Tripp-Lite Isolation Transformer (500 Watts) for years now, and I find it indispensable. Yet, although it is very useful in filtering noises coming from the mains, I'm not sure if it will work as a "humming blocker". It essentially isolates the mains from your gear through the transformer's secondary terminals. The issue is if the humming originates in your audio system's circuit or elsewhere. If it is the latter, it will work. BTW, I've never experienced any audible humming.

You wouldn't, if you use the amp as intended with speakers. Which is what I do 95% of the time. I made myself a speaker taps to 4pin xlr adapter, so I could use the FB with my hd800.

I've actually talked to Dennis about this at some length in the past. He said it's because of the space limitations, he had to wire the right channel by the PSU, thus creating the hum. Again, can only be heard if using headphones, which are many times more sensitive than speakers.

I also own his headamp design iha1, but unfortunately while great, doesn't recreate the magic of the FB. I already have word he's working on a new head-amp though, which I'll be getting to replace the iha1.

At the end of the road, the FB hum is my issue as I'm not using the amp as intended. More than anything, I just found it curious that load on the house circuit removed the hum.. still got me thinking how to replicate that...

I actually already own a Triplitt isolator and a double conversion UPS as well, neither of those fixes the hum. I've thought about trying to rewire the right channel not close to the PSU, but Dennis epoxied all the wires in the amp, so eh. It really is whatever, as the FB is running my Omega Alnico speakers 95% of the time. Just gotta wait for that new headmap design.

Like I said, if the hum originates in your audio circuit the isolation transformer won't fix it.

Classical music dynamics
 

A question to those of you enjoying classical music, especially large orchestral selections. There are evident limitations with flea-powered amps, like our otherwise excellent Inspire units, when playing those intense but certainly essential "tutti" passages.

My question relates to what are some of your suggestions to alleviate those limitations, be it the use of larger tubes, specific rectifiers or even speaker alternatives. There may not be much more we can do, but I'm curious to know what do you guys suggest.

The "oomph" factor required when representing climaxes in this genre is an essential cue in the composer's musical message. This consideration has made me consider SS alternative amplification, but I resist loosing the traits of my Inspire-based system, even when playing classical music. Thanks for any feedback.

Using my higher powered Inspire KT88, the 17 wpc version w/20w output transformers, with KT120 output tubes and GZ34 rectifier, thus maximizing output power, into my 91dB speakers. I find that this combo falls short on classical music at higher volume levels. There just isn't enough power to faithfully reproduce cresendos, deep organ notes (a la Bach), tympani drums, etc.

I think the only path is to have truly efficient speakers. And I mean truly efficient. Many speakers are sold today with efficiency ratings of 95-97dB and yet are really 91-92dB, essentially the same as mine, which truly met their 91dB spec. This include speakers from Zu and DeVore. Even the expensive DeVore O/96 measures at 91dB.

I love listening to artists like Dianna Krall, Holly Cole, Bob Dylan, Norah Jones, CSNY, Sade, and more on my system. They sound so natural. The sound is mesmerizing. The Inspire is incredible on such material. But not so on classical or hard rock.

Do you use that same tube configuration for the less demanding vocal/acoustic selections? I wonder if it would be worth it to get into KT-120's, but as you pointed out, these would probably won't do the trick either. My speakers are theoretically 98 dB/W/M but I suspect these are more like 95 dB/W/M given their impedance distribution.

The idea of much higher sensitivity speakers (i.e., 104 dB/W/M, or so) has intrigued me for some time, although these unavoidably incorporate some type of horn driver design and the affordable horn-type speakers tend not to be that impressive. It's either that or go back to sand power at lower SQ levels.

I do use my KT120/GZ34 combo for all types of music, however I sometimes sub in other output tubes - KT77, KT88, KT66, 6L6GC, 6CA7. Also sub in a 5U4GB from time to time. I haven't yet decided what my favorite combos are, and for what types of music. Narrowing it down. Just got some Gold Lion KT77s, so now I've further muddied up my choices. Had a pair of JJ KT77 before this. I do like the GL KT88s a lot.

Wish my speakers were 95dB. That would make my 17 wpc Inspire sound the equivalent of a 40 wpc amp with my 91dB speakers. I suspect you have a 12 wpc Inspire, that is the standard model. Still a 12wpc with a 95dB speaker will be louder than my 17wpc - 91dB combo.

As discussed here several times, you can get more out of these amps if you use a powered subwoofer. Both of my Inspire amps struggle to produce loud deep bass, going into clipping well before they clip in the midrange. When I filter off sub-80Hz frequencies from my amp, it runs like it is twice as powerful. I've been surprised how loud it can play in that configuration. Still, it is really taxed by classical music cresendos. When played at concert levels, those can need a couple hundred watts on peaks - unless one has very efficient speakers.

Some of those big Klipschs measure at around 104dB. That means they need 1/20th the power that my 91dB speakers require. Down side is that you then have to listen to Klipschs all the time. :)

My HO amp sings with my supposed 91db speakers, helped along by 2 REL subs…no filters on the amp…with plenty of dynamic volume level sent to my earballs 8 feet or so away. This is good news, and I know about concert level sound as I've mixed live concerts professionally for decades (often at disturbingly loud levels…but clean…ya know?). Also, since the HO showed up I've been tube rolling the bejeezus out of it and have decided that for my rig the Gold Lion KT88s, Amperex 6SN7GTB, and Shuguang 274B are the winning combo…KT77s don't have the sizzle I demand (DEMAND!) but they're JJs and not GLs so maybe that makes a difference.