Upgrading my Dared VP-300B Tube Amplifier

[Hari Iyer]

After experiencing the effects of using Audiophile grade components in my Metronome TQWT speakers, i am now contemplating similar upgrades in my tube amplifier shortly. Currently i am in the lookout for components that will fit the bill and will do so only if i can get all of them for the mod.

I will be replacing one wire wound resistor (Inductive Type) with a Non-inductive type. This is a 1Kohm, 15 watts type which is the most difficult to get in non-inductive type. So i am getting it custom made.

Other component is a 100mfd, 250V Electrolytic Capacitor which will get replaced from Jamicon to Vishay BC.
One 0.047mfd, 250V capacitor is also somewhat tricky to procure and could not find any in the usual sites, so planning two 0.022mfd in parallel. This will be changed from MKT to MKP (Polyproplene film - Audio grade)
Another component is two 0.47mfd capacitor (MKT) to Audiograde Metalized Polyproplene Film from Audyn.

These mods are planned over next one to two month time period. Will post outcome after the mods.

Thanks for looking.

 

[Hari Iyer]

After a long pause, i will be planning this upgrade this month. The Jamicon capacitor will be replaced with a high ripple current, long life (12000 hrs) Rubycon capacitors, the MKT type capacitors gets replaced by a metallized Polyproplene film (Audyn) capacitors.

I have already replaced the 12AU7 with the Tung Sol some 3 years ago. The only modification which i will do will be change the 300Bs at the end of their life cyle which i think will be couple of years away

 

[Hari Iyer]

I finally decided to skip the MKP type Audyn capacitors and will instead get a military grade (ROhmb symbol) Russian PIO (Paper-in-oil) foil type capacitors.

 

[Hari Iyer]

So these are the final modifications that i will perform on my 300Bs,

Cathode bypass capacitors - Jamicon to be replaced by Rubycon (same value 100uf, 250 volts)
Coupling capacitors - unbranded MKT type to be replaced by Russian K42y-2 PIO (Same value 0.47uf, 250 volts - only type change)
Cathode resistor - this is under rated (15 Watts) which will be replaced by Alunimum finned 50 Watts of the same value. (1Kohm)

Plate voltage = 320 Volt, Grid Bias = -60 volts.
Cathode current = 60mA.
So the dissipation factor is either 15.6 watts (considering the -60 volts of grid bias) or 19.2 watts (without the Grid Bias). Hence the cathode resistor needs replacement.

Total replacement cost Rs.1500/-.

I am expecting the above to be completed in another months time.

Thanks for looking.

 

[Hari Iyer]

Will be adding couple of more tweaks as below,

- the cathode by pass-capacitor will get another 6.8uf MKP bypass capacitor in parallel.
- will also decouple the output transformer primary by adding a 0.47uf, 600V MKP capacitor from the B+ primary winding to both the filaments to shortcut the anode-cathode signal path. I still have to trace if there is any anode-cathode connection in my amp.

 

[Hari Iyer]

Also will add another 6.8uf, MKP capacitor between the B+ and ground for better dynamics.

 

[Hari Iyer]

I still have to trace if there is any anode-cathode connection in my amp.

There is one 0.047uF,400V MKT WIMA capacitor between B+ and ground.

 

[Hari Iyer]

Will add an Ultrapath with a 33uF capacitor from B+ to cathode resistor. This will introduce power supply noise albeit at a lower level to the cathode which gets amplified at the plate, and will eventually cancel out with the B+ power supply noise due to reverse phase. The net result will be very low noise floor at the output transformer secondary.

 

[Hari Iyer]

Did the stage 1 modifications for the following,
- Replace cathode bypass capacitor
- Added one 4.7uf and 0.47uF capacitor (MKP) parallel to the cathode bypass capacitor.
- Added one 6.8uF MKP capacitor to B+ and ground.
- Added one 30uF MKP capacitor from B+ to cathode resistor (Ultrapath)

Balance pending modifications,
- Replace cathode resistor
- coupling capacitor

So how do they sound -
Well the difference is night and day )100%) similar to replacing the stock shaugaug 300Bs with vintage WE300Bs (2 more mods are still pending).
- Increased sound stage by leaps and bounds
- midrange clutter and power supply noise vanished like its in a different world
- Highs are now rounded without any harshness, very very sweet highs like real instruments.

Am now wondering why i waited so long for this simple modifications all these years.

Attaching images for all to check the size of the capacitor.

Thanks for looking

 

[jls001]

So it's worth the effort and money

Good bypass caps work wonders. That has been my experience in my speakers too.

 

[Hari Iyer]

So it's worth the effort and money

Good bypass caps work wonders. That has been my experience in my speakers too.

Yes more than 100% effort worth. Its like buying a new 300B - Vintage Western Electric tube. Now i can say, that i have some experience in identifying the power supply noise.

@ Viren Bakshi - if you happen to read this post, you should consider these in your 300Bs - especially the Ultrapath for the day and night difference.

 

[Hari Iyer]

Many have suggested me to change the stock AC power input cable for the amp. I am going by their wisdom and will be changing the puny AC input cable. I will be twisting three 2.5 sq.mm polycap cable for the line, neutral and earth and may be put them inside a sleeve. Its observed by others that midrange has body and the bass tight with this simplistic mod.

 

[Hari Iyer]

Plate voltage = 320 Volt, Grid Bias = -60 volts.
Cathode current = 60mA.
So the dissipation factor is either 15.6 watts (considering the -60 volts of grid bias) or 19.2 watts (without the Grid Bias). Hence the cathode resistor needs replacement.
.

There was a calculation issue in the above,
The dissipation factor is 3.6 watts ( 60*0.06), So the 15 watts resistor should be enough in the setup. But as i have already purchased them, i will rather go ahead and install it.

 

[keith_correa]

Many have suggested me to change the stock AC power input cable for the amp. I am going by their wisdom and will be changing the puny AC input cable. I will be twisting three 2.5 sq.mm polycap cable for the line, neutral and earth and may be put them inside a sleeve. Its observed by others that midrange has body and the bass tight with this simplistic mod.

Take 4 Polycab wires. Tightly twist two each for two twisted pairs. From each pair take 1 wire each, connect them to each other and use that for earth. Use the remaining two wires for live and neutral respectively. Encase both twisted pairs in a tight sleeve. The longer the run, the better this works.

 

[Hari Iyer]

Take 4 Polycab wires. Tightly twist two each for two twisted pairs. From each pair take 1 wire each, connect them to each other and use that for earth. Use the remaining two wires for live and neutral respectively. Encase both twisted pairs in a tight sleeve. The longer the run, the better this works.

Thanks for the tip. Will do as suggested by you.

 

[Hari Iyer]

One more planned mod for the future is replace the outdated 1N4007 rectifier diode used to power the 300Bs / 12AU7 plates with the UF4007 (Ultra Fast series) didoes to make them more relevant to present scenario.

 

[Hari Iyer]

My upgrades to the 300B took me a different route last week. I focused on internal wiring of the amplifiers and how they affect the sound stage. I started examining them one by one and thought of replacing wherever possible -

Original wires -

Input signal cables are - signal hot - stranded copper cable - cold is shielded cable

Power supply cables = extremely thin 4 to 7 stranded copper cable wpuld be less than 24 SWG for all - ie. B+, Directly heated and indirectly heated triodes and ground wires. The B+ and ground are dual wires (giving me some relief). Whenever by accident i switch on the power module without connecting the load (power amplifier) and later connect them this will give a spark and all the wires would get burnt. This will give an indication how thin this wire is.

I wanted to replace all these cables both in the power supply module and power amplifier module but did not gather courage due to nonavailabiity of wiring or circuit diagram. Last week gathered some courage and went on to replace only in the power supply module.

The choice of wire for replacement from thin stranded copper wire to silver plated copper teflon wire all of 18SWG. I carefully redrew the wiring and connected everything ( B+, DHT, IDHT, Ground, Earth - total of 8 wires per channel). After listening the amplifier became hell of bright, loosing focus, increased SPL, loss of sound stage and very fatigue. This was with only the power supply wire replacement.

I went on to research further and with the link provided by Prem checked the recommendations from experts. There is a whole lot of debate on which wires should be used where and there is never an agreement in any forums. So today morning, i again went ahead to replace the teflon cables with single core pure copper conductor enameled magnetic wire.

The choice of wires - B+ 22 SWG - Dual core - so it makes it 16 SWG (380 V DC)
Ground 20 SWG - Dual core - so it makes it 15 SWG
DHT 20 SWG (5 v AC)
IDHT 22 SWG (6.3v AC)

input cables - 22 SWG - hot signal straight - cold twisted on the hot - single core conductor.

Note: All wires are enameled and not sleeved. Only termination has glass fiber sleeve.

This replacement restored the balance of the sound stage and removed the shrill and brightness from the sound stage and now it sounds even better than the thin stranded copper wires.

Now my plan is to also do this replacement in the poweramps and see how much of a benefit it can draw from this. But this is for a long weekend week.

Overall lots of learnings in interconnects and internal wiring last week and time well spend discussing the same.

Thanks for looking.

 

[Hari Iyer]

Yesterday i experimented with Ferrite beads on the cables as below,

I have a power module which supplies AC & DC supplies to the power amplifier connected through a 8 pin umbilical chord between them.
The following voltages goes from the power module to the power amplifier (Left and Right)

- B+ 380 volts DC
- 6.3 volts AC for the DHT
-6.3 volts AC for the IDHT
- Ground.

I added a Ferrite choke strap on on these power cables and noticed better dynamics in the sound stage. The amp became dead silent in between tracks and the sound stage became more easy to the ears with all the power supply background noise vanishing. I cannot explain why, but since the AC signal will be around 50Hz and the DC close to 0 Hz, any RF or EMI noise picked up by the cable gets removed by the ferrite and a cleaner power goes to the power amp now.

Also my coaxial digital cable from the DAC to the CD player where the SPDIF connection goes has 2 ferrite beads at either ends of the cable. This has done nothing to the audio frequency but helps to keep the RF & EMI noise away from the digital signal. Any RF/EMI emitted by the CD player will get sucked out by the ferrite from the coaxial cable.

The ferrites begin to show its affect only after around 4 MHz to 5MHz freq range. The SPDIF has a sampling freq of 44.1KHz with a 16 bit rate it goes till 2.3MHz. Hence these signals anyway is out of the range of the ferrite bead and will not be attenuated in a negative way.

I think over using ferrites could cause more harm, but careful use of ferrite beads are good for audio. I would not adivse using ferrites in the analogue cables or the AC mains input though for transformer based devices like amplifiers. Maybe for CD player / Blue-ray player / DVD player where SMPS power supply exist, ferrite bead on the AC cable could be of some help.

 

[Hari Iyer]

There are around 16 resistors in my 300Bs and out of this one is wire wound (cathode resistor), one is carbon composite and rest are smd (probably metal film or carbon film resistors).
I always wanted to change the smd type resistor to some other type (not able to decide).
I have been reading in the net and many projects use carbon composites for grid stopper (output stage), metal film (grid lekage) and a combination of metal film or wire wound resistor else where.
But many are also of the opinion that carbon composites fail and the value drift over time and are not to be used.

I am contemplating to replace all the 14 smd resistors with 3 watt wire wound resistors of the same values. The main issue with wire wound resistors are they are difficult to get in high values and they require a high wattage type to operate at 300+ volts. The 3 watts resistor can be used only till around 100 volts and you require atleast a 6 watt resistor for 400v operation. Also most of these resistors are needed to be custom built. Fortunately i have found 3 to 4 companies in Mumbai who built wire wound resistors and will be contacting them with my values.

These resistors will be silicon coated with cu-ni and tin plated copper ends. Hope they give for small quantity required for me.

Wire wound resistors were selected over metal film, metal oxide, carbon film and carbon composite types. Bulk metal foil was out of question due to huge unreasonable price. The wire wound has the least noise figure compared to all the other types. The only issue being the inductance it can have. I measured a 1Kohm wire wound resistor and found it inductance to be in the 100uH region which is way beyond the audio frequency range to influence any oscillation (having some inductance is good for RF blocking). In the critical grid stopper section i shall prefer to use a non-inductive type.

All depends upon the component availability and the skills of the manufacture of these resistor to support my fantasy.

 

[Ravindra Desai]

There are around 16 resistors in my 300Bs and out of this one is wire wound (cathode resistor), one is carbon composite and rest are smd (probably metal film or carbon film resistors).
I always wanted to change the smd type resistor to some other type (not able to decide).
I have been reading in the net and many projects use carbon composites for grid stopper (output stage), metal film (grid lekage) and a combination of metal film or wire wound resistor else where.
But many are also of the opinion that carbon composites fail and the value drift over time and are not to be used.

I am contemplating to replace all the 14 smd resistors with 3 watt wire wound resistors of the same values. The main issue with wire wound resistors are they are difficult to get in high values and they require a high wattage type to operate at 300+ volts. The 3 watts resistor can be used only till around 100 volts and you require atleast a 6 watt resistor for 400v operation. Also most of these resistors are needed to be custom built. Fortunately i have found 3 to 4 companies in Mumbai who built wire wound resistors and will be contacting them with my values.

These resistors will be silicon coated with cu-ni and tin plated copper ends. Hope they give for small quantity required for me.

Wire wound resistors were selected over metal film, metal oxide, carbon film and carbon composite types. Bulk metal foil was out of question due to huge unreasonable price. The wire wound has the least noise figure compared to all the other types. The only issue being the inductance it can have. I measured a 1Kohm wire wound resistor and found it inductance to be in the 100uH region which is way beyond the audio frequency range to influence any oscillation (having some inductance is good for RF blocking). In the critical grid stopper section i shall prefer to use a non-inductive type.

All depends upon the component availability and the skills of the manufacture of these resistor to support my fantasy.

Hari,

Why wire wound over metal film?
Also, at the level of sensitivity you are working, changing from SMT to leaded type components introduces undesirable lead inductance. Like wise, any low inductance wire-wound resistor is still large added inductance over the SMT type.
Kindly be aware.

Regards,

Ravindra.