[Bosk]

I don't think there's a cross reference / replacement tube for the JAN5899.
But, there are some eBay vendors who sell "matched" sets of JAN5899 tubes.

I found these Sylvania/s on eBay (it isn't clear if he has more than one) which look interesting:
https://www.ebay.com.au/itm/Vintage...u-Pentode-Valve-BangyBang-Tubes-/274082978998


Do you mind if I ask a question about resistors?

I measured all 10 B4-X fixed resistors -albeit with a cheap multimeter- and their values are: 2.5k ohm (x2) 118k ohm (x2) 25 ohm (x4) and 30k ohm (x2).
I'd like to replace them with Caddock MK232 which replace the excellent MK132's I've used in the past, but they aren't available in the exact values. Do you think their values would be "close enough"?
Default values are: 25, 2.5k, 30k and 118k - whereas Mouser have MK232's in the closest values of 20, 2k, 50k, and 100k.

Otherwise I could use Caddock MP930 resistors which come in 25, 2.5k, 30k and 125k, but they are TO-220 package and there isn't a lot of room on the board, plus the leads are thick. There may be other brands of small form factor high-end resistors that are a major upgrades on the (Dale?) resistors the amp comes with that I'm not aware of.

https://au.mouser.com/Passive-Compo...-Through-Hole/_/N-7gz43?Keyword=MK232&FS=True
https://au.mouser.com/ProductDetail/Caddock/MP930-250-1?qs=d6ViQafmxQTraVb%2BhhZS4A==

 

[DBaldock9]

While I knew about the Raytheon JAN5899, since it's being used in the Little Bear B4 & B4-X, I noticed that there's a surprising number of other Subminiature Pentodes, including Russian Military tubes, available on eBay.
Link to a copy of the Raytheon JAN5899 datasheet - https://frank.pocnet.net/sheets/138/5/5899.pdf
Link to an interesting thread about Russian Subminiature Tubes, on the RadioMuseum Forums - https://www.radiomuseum.org/forum/russian_subminiature_tubes.html
It would be interesting to find out whether the power supply circuit in the B4-X would work with some of those Russian tubes.
.
I've never done any indepth research on resistors - but I thought that Dale was a good brand for audio gear.

 

[Bosk]

A bit like Wima film caps, Dale resistors are ofted used on cheap entry-level gear from China. I suspect its because they've earned some recognition in the DIY community as an affordable choice that performs decently.

Unfortunately I'm an audiophile and "decent" performance has never satisfied me! I've replaced Dale resistors with MK132's and Vishay Z-Foils in the past and the difference has been tremendous when substituting resistors in the signal path. Unfortunately I don't have a schematic for the B4-X so I'm not sure which of those 10 resistors are in the signal path, it probably won't make much of a difference replacing those that aren't. Of course the film caps would ideally be upgraded too but there's so little room on the board in that region, and any high-end 2.2uF film caps like Mundorf Supremes would as wide as the board itself.

What I have found from my experiments in the past is that the more you improve and upgrade a piece of audio gear the more cumulative benefit is incurred from each improvement. So replacing those films caps for instance might not be worth it on a stock B4-X board but if everything else were upgraded beforehand then the difference in doing so would be more noticable and therefore worthy of the time & expense.

 

[Bosk]

I'm still waiting for parts to arrive, would there be any sonic advantage from powering each tube and op-amp from a separate regulator & supply caps?

 

[DBaldock9]

I'm still waiting for parts to arrive, would there be any sonic advantage from powering each tube and op-amp from a separate regulator & supply caps?

I suspect that improving the power supplies can help the audio performance.

 

[Bosk]

I suspect that improving the power supplies can help the audio performance.

I think you're right. I'll start investigating options then.

 

[Bosk]

The Burson V6 Vivid op-amps arrived today! The improvements over the V5i-Ds are immediately obvious, everything sounds noticably smoother with a layer of grit previously present wiped away, there's a greater feeling of precision and musicality, and the soundstage feels satisfyingly deeper. I feel much more emotionally connected with the music, particularly evident with midrange vocals.

Despite the difference in price they are undoubtedly worth the extra expense, that aside the only downside -according to the datasheet- is increased power draw, but for that I've connected a new 12V 5500mAh battery which should ensue all-day playback. I've also installed some extra power supply caps on the back side of the board but they didn't seem to make much difference. Suffice to say the amp won't be winning any beauty contests in its present state, eventually I'm thinking of re-housing it in a DIY perspex case which should be easier to construct than most other options.

 

[SBMonster]

The Burson V6 Vivid op-amps arrived today! The improvements over the V5i-Ds are immediately obvious, everything sounds noticably smoother with a layer of grit previously present wiped away, there's a greater feeling of precision and musicality, and the soundstage feels satisfyingly deeper. I feel much more emotionally connected with the music, particularly evident with midrange vocals.

Despite the difference in price they are undoubtedly worth the extra expense, that aside the only downside -according to the datasheet- is increased power draw, but for that I've connected a new 12V 5500mAh battery which should ensue all-day playback. I've also installed some extra power supply caps on the back side of the board but they didn't seem to make much difference. Suffice to say the amp won't be winning any beauty contests in its present state, eventually I'm thinking of re-housing it in a DIY perspex case which should be easier to construct than most other options.

Does the battery fit into the housing ?

 

[SBMonster]

Hi everyone!
Did anyone tried to pair this amp with Senn’s hd 560s?

 

[Bosk]

Does the battery fit into the housing ?

The new 5500mAh battery doesn't, I'll need to build a new case to house it and the PCB. It would be almost impossible to fit a battery larger than the default in the original case.

 

[DBaldock9]

The new 5500mAh battery doesn't, I'll need to build a new case to house it and the PCB. It would be almost impossible to fit a battery larger than the default in the original case.

Unless you have a convenient local supplier, here's a handy AliExpress shop with a wide selection of Aluminum enclosures - https://www.aliexpress.com/store/418985

 

[Bosk]

Unless you have a convenient local supplier, here's a handy AliExpress shop with a wide selection of Aluminum enclosures - https://www.aliexpress.com/store/418985

Some of those look quite smart, thanks for the link. I do tend to wonder if there'd be any sonic benefit in terms of shielding by using a metal enclosure rather than something simpler such as sandwiching the board between two sheets of perspex separated by PCB standoffs.

 

[Bosk]

So @DBaldock9 have you tried decoupling your op-amps yet?

I'd like to give it a try and have some Wima 0.1uF film caps on hand, but the article on Burson's website is slightly confusing and I'm not exactly sure which pins they should be soldered to:

https://www.bursonaudio.com/burson-ss-opamp-101-part-1-mkp-cap-tweak/

 

[DBaldock9]

So @DBaldock9 have you tried decoupling your op-amps yet?

I'd like to give it a try and have some Wima 0.1uF film caps on hand, but the article on Burson's website is slightly confusing and I'm not exactly sure which pins they should be soldered to:

https://www.bursonaudio.com/burson-ss-opamp-101-part-1-mkp-cap-tweak/

I did install the pairs of Ceramic & Tantalum caps on the back of B4-X circuit board, back in May. They're connected to the V+ and V- pins of the op-amp sockets.
.

 

[Bosk]

I did install the pairs of Ceramic & Tantalum caps on the back of B4-X circuit board, back in May. They're connected to the V+ and V- pins of the op-amp sockets.
.

Very nice, did you notice much improvement? May I also ask if there's any particular benefit to star grounding them?