Dennis Had Inspire Amps

[x3workshop]

Originally Posted by FloridaBoy

What tubes are you running? With 6L6 or 6V6 tubes mine does not get very hot. I believe we have the same amp.

KT88's & KT120's w/5AR4.

[FloridaBoy]

Originally Posted by Twanny

KT88's & KT120's w/5AR4.

Yeah, that would be a hot combination. I bought some NOS, made around 1999 or so, Full Music 274A perforated plate rectifiers for $50 each and have sort of forgotten about my other rectifiers except 80's.

[MWalt]

Originally Posted by robert_kc

I think that the Klipsch RF-7 II is an excellent value. When carefully matched with an amp they can achieve a natural sound. (I use a variety of tube amps.) And they are able to handle the dynamics of opera and large scale classical music. They’re not as nice looking as the Palladium, but they’re much less expensive.

Which version of the Firebottle amp do you own? (Apparently there are many variations, and its difficult for me to figure out who owns which amp. Perhaps we should include a brief description of our amp whenever we share our observations about its performance.)

BTW, I'll listen to mine sometime later today, and I will check the transformers for their temperature.

I have the Fire Bottle KT-88 and LP-2 Preamp. Currently running GE 6L6GC's and a Philips 5R4GYS rectifier (changes weekly, LOL). I' ve been thinking about trying some new high efficiency speakers and was interested in yours.

[robert_kc]

Regarding the heat issue, the transformers in mine get only slightly warm.

My understanding is that there are many different versions of the Fire Bottle amp. Mine was built in October 2015. Here’s Dennis’ description:

INSPIRE TUBE AMPLIFIER by DENNIS HAD FEATURING THE KT-88/6550 BEAM POWER VACUUM TUBE AMPLIFIER IN A SINGLE-ENDED CLASS A SET TRIODE DESIGN

• CLASS A, 8 WATT, ZERO-FEEDBACK TRIODE
• KT-88 GENALEX OUTPUT TUBES
• 6CG7 NOS INPUT DRIVER
• 5U4 Shuguang RECTIFIER TUBE
• REGULATED DC, B+ VOLTAGE ON DRIVER TUBE
• REGULATED DC POSITIVE CATHODE BIAS ON DRIVER TUBE
• CUSTOM DESIGNED AIR-GAP 15 WATT OUTPUT TRANSFORMERS TO MATCH KT-88 TUBES IN THE TRIODE MODE
• This power transformer is capable of powering four (4) of these amplifiers. 24/7 continuous duty design.
• I have designed and built in just about every special part but the kitchen sink in this TRIODE "Fun-Amp"
• The amp plays like a 25 watter with amazing control and slam. I consider this a "life-time" amplifier.

Perhaps different units have different transformers?

As I said earlier, here’s the tubes that complement my Klipsch RF-7 II speakers:

• Substitute Groove Tube Gold Series GT6L6 GE (performance rating 5) for KT88
• Substitute 6DJ8 for the 6CG7
• Substitute 6Z34 / 5AR4 for 5U4

The only shortcoming is inadequate gain for high-res classical recordings (which are recorded at relatively low volume levels) when driven directly by my Oppo universal player. OTOH, for big band music this configuration and my Klipsch RF-7 IIs sound fantastic and play plenty loud.

Has anyone tried the new-production Tung-Sol 7581A in this amp? Here’s a description: “This tube is an upgraded 6L6GC tube but will provide more headroom than typical 6L6GC tubes. The 7581-A tube has a plate dissipation rating of 35W, as opposed to the 6L6GC and 7581 rating of 30W. The 7581A tube can be used in any 6L6 based tube circuit.” I’m skeptical that this will provide any improvement vs. the GT6L6 GE that I like in this amp – I’m looking for more gain, not more power.

FWIW I tried a pair of KT66 and found them to be a little bright for my speakers.

[FloridaBoy]

Originally Posted by robert_kc

Regarding the heat issue, the transformers in mine get only slightly warm.

My understanding is that there are many different versions of the Fire Bottle amp. Mine was built in October 2015. Here’s Dennis’ description:

INSPIRE TUBE AMPLIFIER by DENNIS HAD FEATURING THE KT-88/6550 BEAM POWER VACUUM TUBE AMPLIFIER IN A SINGLE-ENDED CLASS A SET TRIODE DESIGN

• CLASS A, 8 WATT, ZERO-FEEDBACK TRIODE
• KT-88 GENALEX OUTPUT TUBES
• 6CG7 NOS INPUT DRIVER
• 5U4 Shuguang RECTIFIER TUBE
• REGULATED DC, B+ VOLTAGE ON DRIVER TUBE
• REGULATED DC POSITIVE CATHODE BIAS ON DRIVER TUBE
• CUSTOM DESIGNED AIR-GAP 15 WATT OUTPUT TRANSFORMERS TO MATCH KT-88 TUBES IN THE TRIODE MODE
• This power transformer is capable of powering four (4) of these amplifiers. 24/7 continuous duty design.
• I have designed and built in just about every special part but the kitchen sink in this TRIODE "Fun-Amp"
• The amp plays like a 25 watter with amazing control and slam. I consider this a "life-time" amplifier.

Perhaps different units have different transformers?

As I said earlier, here’s the tubes that complement my Klipsch RF-7 II speakers:

• Substitute Groove Tube Gold Series GT6L6 GE (performance rating 5) for KT88
• Substitute 6DJ8 for the 6CG7
• Substitute 6Z34 / 5AR4 for 5U4

The only shortcoming is inadequate gain for high-res classical recordings (which are recorded at relatively low volume levels) when driven directly by my Oppo universal player. OTOH, for big band music this configuration and my Klipsch RF-7 IIs sound fantastic and play plenty loud.

Has anyone tried the new-production Tung-Sol 7581A in this amp? Here’s a description: “This tube is an upgraded 6L6GC tube but will provide more headroom than typical 6L6GC tubes. The 7581-A tube has a plate dissipation rating of 35W, as opposed to the 6L6GC and 7581 rating of 30W. The 7581A tube can be used in any 6L6 based tube circuit.” I’m skeptical that this will provide any improvement vs. the GT6L6 GE that I like in this amp – I’m looking for more gain, not more power.

FWIW I tried a pair of KT66 and found them to be a little bright for my speakers.

These amps do have different transformers. Dennis has them wound at a shop near him. FWIW, Twanny and I have 20 watt transformers.

The 6CG7 is a 6SN7 in a smaller bottle. If your amp has room you can get an adapter and use 6SN7 tubes.

Which KT66's were you using?

[MWalt]

I wonder what I would have to do to get him to change out my PT with a much bigger one?

[robert_kc]

Originally Posted by FloridaBoy

These amps do have different transformers. Dennis has them wound at a shop near him. FWIW, Twanny and I have 20 watt transformers.

The 6CG7 is a 6SN7 in a smaller bottle. If your amp has room you can get an adapter and use 6SN7 tubes.

Which KT66's were you using?

FloridaBoy,

Thanks for the information.

I didn’t have any spare KT66 in my inventory, so I pulled a pair from one of my Pilot HF-56 (which is a fabulous sounding mono receiver from the 1950s). I didn’t look at the labeling – I think that these KT66s are inexpensive Chinese tubes. My assessment: If someone finds that 6L6GC sound too dull in their amp, they might try KT66. (I’ve also tried KT88 and EL34, which were OK, but not to my liking.)

With my current tube complement, I have the tonal balance that I want with my amp and speakers. My only problem is with the input sensitivity of the amp (i.e., how strong of an input signal is required to drive the amp to satisfactory output level). I tried 6CG7 (originally equipped) and 6N1P-EB and 6DJ8, and found that I like the 6DJ8 best thus far (i.e., most gain and best sound).

I didn’t know that a 6SN7 could be substituted via an adapter. If it is electrically equivalent to the 6CG7, I’m skeptical that it would have any more gain. OTOH, I found eight various 6SN7GTB in my inventory, so I could do plenty of tube rolling. (Of course I’d then feel compelled to try the 6SN7 with many different output tubes, leading to another round of tube rolling. Oy vey … )

Has anyone found a seller for the 6SN7 to 6CG7 adapter based in the USA? (I found sellers in Hong Kong and China.) Perhaps the adapter would open up the possibility to use other input tube types that have more gain? I don’t want to go too far afield and substitute a different type of tube that Dennis hasn’t approved. Am I correct based on earlier posts in this thread that owners of some other Inspire amp variants have swapped 6SN7 and 6SL7? Does anyone know if this is safe for my amp, and if so would it result in more gain? (I’ve read that in theory the 6SL7 has more gain than the 6SN7.)

Has anyone heard an update from Dennis about his tube chart?

As I’ve said before, the reason that I’m interested in increasing the input sensitivity is that I like the idea of using the Inspire amp without a preamp (i.e., a “minimalist” configuration). With some recordings I’m able to achieve excellent sound this way. (And, I do this in other systems with my McIntosh MC30s, MC240, and Pilot SA-260.) With the Inspire amp direct connected to one of my Oppo universal players, I need to advance the Oppo’s volume level to approximately 75% for big band music. For high-res classical recordings I realize marginally adequate volume with the Oppo’s output set to 100%. So, I need just a little more “oomph” from the input stage of the Inspire. Or perhaps the next-gen Oppo player (expected late 2016) will have higher output level. Or perhaps Dennis will offer a different variant of the Inspire amp with greater input sensitivity …

Thanks again for your assistance.

[pstrisik]

Robert,

An option is to try a russian 6N2P. I asked Dennis about it in March of 2015 and he said:

Greetings from snowy, Cary, NC. I would say give the 6N2P a try. I have not listened to this tube but it should work just fine. It should have a bit more gain.

You can get them dirt cheap on the bay.

[FloridaBoy]

Originally Posted by robert_kc

FloridaBoy,

Thanks for the information.

I didn’t have any spare KT66 in my inventory, so I pulled a pair from one of my Pilot HF-56 (which is a fabulous sounding mono receiver from the 1950s). I didn’t look at the labeling – I think that these KT66s are inexpensive Chinese tubes. My assessment: If someone finds that 6L6GC sound too dull in their amp, they might try KT66. (I’ve also tried KT88 and EL34, which were OK, but not to my liking.)

With my current tube complement, I have the tonal balance that I want with my amp and speakers. My only problem is with the input sensitivity of the amp (i.e., how strong of an input signal is required to drive the amp to satisfactory output level). I tried 6CG7 (originally equipped) and 6N1P-EB and 6DJ8, and found that I like the 6DJ8 best thus far (i.e., most gain and best sound).

I didn’t know that a 6SN7 could be substituted via an adapter. If it is electrically equivalent to the 6CG7, I’m skeptical that it would have any more gain. OTOH, I found eight various 6SN7GTB in my inventory, so I could do plenty of tube rolling. (Of course I’d then feel compelled to try the 6SN7 with many different output tubes, leading to another round of tube rolling. Oy vey … )

Has anyone found a seller for the 6SN7 to 6CG7 adapter based in the USA? (I found sellers in Hong Kong and China.) Perhaps the adapter would open up the possibility to use other input tube types that have more gain? I don’t want to go too far afield and substitute a different type of tube that Dennis hasn’t approved. Am I correct based on earlier posts in this thread that owners of some other Inspire amp variants have swapped 6SN7 and 6SL7? Does anyone know if this is safe for my amp, and if so would it result in more gain? (I’ve read that in theory the 6SL7 has more gain than the 6SN7.)

Has anyone heard an update from Dennis about his tube chart?

As I’ve said before, the reason that I’m interested in increasing the input sensitivity is that I like the idea of using the Inspire amp without a preamp (i.e., a “minimalist” configuration). With some recordings I’m able to achieve excellent sound this way. (And, I do this in other systems with my McIntosh MC30s, MC240, and Pilot SA-260.) With the Inspire amp direct connected to one of my Oppo universal players, I need to advance the Oppo’s volume level to approximately 75% for big band music. For high-res classical recordings I realize marginally adequate volume with the Oppo’s output set to 100%. So, I need just a little more “oomph” from the input stage of the Inspire. Or perhaps the next-gen Oppo player (expected late 2016) will have higher output level. Or perhaps Dennis will offer a different variant of the Inspire amp with greater input sensitivity …

Thanks again for your assistance.

You're welcome.

The 6CG7 is electrically equivalent to the 6SN7 but if you prefer the 6DJ8 so be it.

You might want consider e-mailing Dennis about a preamp because he designed to be used with one. He can adjust the gain. Or ask him how to maximize the gain.

[x3workshop]

Originally Posted by MWalt

I wonder what I would have to do to get him to change out my PT with a much bigger one?

Ask Dennis to swap it out. I've been thinking the same thing. Just will cost some $$.