tubes 4 hifi
 "the path of least resistance is through a vacuum"
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supplys are running low, order these amps NOW or face possible delays!!

 


ST70 stereo amp

ST120 stereo amp

M-125 monoblocks

customer reviews of our amplifiers

time delay relay


Due to the Covid-19 pandemic and uncertain shipping times to areas outside the USA and Canada,
I am temporarily suspending all sales and shipments to areas outside the USA and Canada.

 


ST70 stereo amp

ST120 stereo amp

M-125 monoblock

these speaker posts are now standard

 

 

NOTE 1 - if you have any questions about any of the 3 amps kits listed on this web page just email me at send email : Bob01605@aol.com
If you want to talk by phone I can email you my phone number for a call.
Payments can be made by cashier's check, money order, or via PayPal. Payments by cashier's check or money order
will receive a $25 discount on a SINGLE amp kit (ST70 or ST120) or a $50 discount on a PAIR of M125 kits.
All wired and tested amps are custom built and shipped out about 2 weeks after receipt of payment.



We now have 1/8 inch acrylic driver board covers in stock for both the VTA ST-70 and VTA ST-120 amp kits.
These driver board covers fit ONLY the 12AU7 CCS board that we have been using since 2012.
They do NOT fit older VTA driver boards (pre 2012) that used 12AT7 driver tubes.

The VTA ST-70/ST-120 driver board cover is out of stock


Driver board cover for your VTA ST-70 or VTA ST-120 - clear finish - $30 (free shipping) if ordered with a VTA amp kit.

Driver board cover for your VTA ST-70 or VTA ST-120 - clear finish - $30 + $5 shipping ($35) if ordered separately from a VTA amp kit.


brand NEW ST70 amplifiers, The VTA ST-70 amp kit is IN STOCK and ready to ship

ST70 amplifier features:

1. The new STAINLESS STEEL chassis is identical in size, shape and markings to the older original nickel plated steel frame. 
   This upgraded chassis is NON-MAGNETIC and removes any magnetic interference effects of a steel chassis on the audio circuitry.
 
2. The new USA made power transformer has a higher stack lamination than the original Dynaco power transformer and is rated 
   for 120 volts instead of 115 like the old design. The two tube heater legs are rated for 5 amps each instead of 3 amps each 
   like the old design. This beefed up transformer (which has a bottom plate like the original PA-060 to prevent EMI from 
   the transformer from reaching the audio circuitry) allows the use of KT88 output tubes in place of the EL34 tubes for 
   a slightly different tonal presentation. Four heavy duty neoprene isolation mounts are used to attach the transformer to the chassis.
 
3. The A-470 output transformers are brand new USA made custom production transformers. They use the same interleaved/layer winding 
   technique as the original cloth lead A-470's and incorporate the same high quality M-6 grain oriented laminations. 
   They are dimensionally accurate to the original design and have a durable heat resistant black epoxy finish.
 
4. The old stock 30, 20, 20, 20 electrolytic quad cap which had marginal storage capacity for this amp has been replaced by 
   a 80, 40, 30, 20 quad cap for almost double the power storage capacity.
 
5. The upgraded VTA driver board uses three new 12AU7 or 12BH7 triodes in place of the two mediocre sounding 7199 pentode/triode tubes. 
   Dynaco saved money using a two tube 7199 board design but made some serious compromises in sound quality.  
   The older ST-70 design had one bias control for each channel whereas the VTA board has a separate bias control for each of 
   the four output tubes. This design allows for individual adjustment of each output tube bias. 
   Matched pairs or quads of output tubes are not necessary with this design. 
   Eight quality Sprague 716P "orange drop" coupling caps are included with the board.
 
6. The input jacks are gold plated and have a wider spacing to allow for newer design thicker interconnects.
 
7. The output jacks are modern gold plated 5 way binding posts.
 
8. The 7 octal tube sockets are modern high quality Celanex sockets with cadmium plated pins. 
   These sockets are very durable and more reliable than the older stock phenolic tube sockets found in the original amps.

9. Includes two triode/pentode switches to allow switching between these two modes of operation. 
   The switching may be done while the amp is running to compare the two sonic presentations.


 

"Shipping costs will be invoiced separately after your purchase of an amp kit - 36 pounds for the ST-70 and 42 pounds for the ST-120.
Kits to the USA are shipped by UPS Ground or USPS Priority Mail.
Shipments to Canada and other countries outside the USA are shipped by USPS Priority Mail International "
Due to the Covid-19 pandemic and uncertain shipping times to areas outside the USA and Canada,
I am temporarily suspending all sales and shipments to areas outside the USA and Canada.


VTA ST70 $769 + shipping IN KIT FORM
with all parts but NO TUBES
VTA ST70 $909 + shipping IN KIT FORM
with all parts and tubes and EL34 output tubes
VTA ST70 $1019+ shipping IN KIT FORM
with all parts and tubes and 6550 output tubes
VTA ST70 $1165 + shipping WIRED with NO TUBES
VTA ST70 $1305 + shipping WIRED with ALL tubes & EL34 output tubes
VTA ST70 $1415 + shipping WIRED with ALL tubes & 6550 output tubes
240 volt operation add $70 to KIT amp price
add capacitor upgrade for $45 (4 Power supply and 4 hand matched Russian K42-Y PIO coupling caps)

A 21 step, stepped attenuator kit to install in place of the unused stereo/mono switch to allow you to use your ST-70 amp without a preamp !
This is a great option if you only have one signal source for your ST-70 like a CD player. The attenuator may also be used WITH A PREAMP.
If you turn the control all the way to the right there is complete pass through of the signal with no attenuation or alteration of the signal.
You may also use the attenuator as a master level control to effectively reduce the gain of the amp.
$50 added to any ST-70
or ST-120 KIT amp
$75 added to any ST-70
or ST-120 WIRED amp

$50 + $5 shipping = $55
for your existing amp

NOTE: price includes shipping inside USA only, for Canada or worldwide, email for shipping cost


 


ST70 amp kit assembled by Bob
the internal wiring with the Triode/Pentode switches

 

For more information or questions about a KIT or WIRED VTA ST-70 or ST-120 amplifier - - - Email me at Bob01605@aol.com

The VTA ST-120 amp kit is OUT of STOCK until about Nov 1st


VTA120 amp !!

For those that need a little more power is the Dynaco VTA ST-120.
 
 
The VTA ST-120 is a 60 WATT PER CHANNEL amplifier built on the same ST-70 stainless steel chassis as the amp pictured above.
The VTA ST-120 uses three custom wound USA made transformers and is available as a KIT amp or completely WIRED and tested.
This amp has the same quality components as the VTA ST-70 listed above. The optional tube set has a GZ34/5AR4 rectifier,
three 12AU7 driver tubes and a matched quad of 6550 tubes.
The power transformer instead of 360-0-360 secondaries like the ST-70 has 420-0-420 secondaries and puts about 485 volts on the plates
(pin 3) of the output tubes. The ST-70 puts about 420 volts on the plates. The stack lamination on this transformers is about 2.70 inches tall
- my ST-70's power transformer stack is about 2.05 inches high. This transformer weighs about 4 pounds more than the ST-70 transformer
and is rated at 425 milliamps of current flow.
The output transformers have 4200 ohm primaries, 40% ultralinear screen taps and are 3 7/8" tall, 3 1/4" wide and 3 1/8" deep
(about 1/2" taller, 3/8" wider and 1/4" deeper than a stock A-470 output transformer). Each output transformer weighs about
2 pounds more than a stock A-470 output transformer.
The power storage caps have a higher capacity and voltage rating than the VTA ST-70.
 

 


The ST120 is an amazing sounding amp! review and comparison with a McIntosh 275 amp

 


 

all ST-70 and ST-120 amp kits come with a heavy duty 16 gauge chassis

customer photo of ST120

"Shipping costs will be invoiced separately - 42 pounds from zip code 01566 by UPS ground"

VTA ST-120 KIT with NO TUBES > $989 + shipping VTA ST-120 KIT with a complete tube set with Sovtek 6550 output tubes is $1239 + shipping
VTA ST-120 WIRED and TESTED amp with NO tubes > $1485 + shipping VTA ST-120 WIRED and TESTED amp with a complete tube set with Sovtek 6550 output tubes > $1725 + shipping

add capacitor upgrade for $45 - (4 Power supply and 4 hand matched Russian K42-Y PIO coupling caps)

 
220/240 volt power transformer for the VTA ST-120 amp kit (add $70 USD)
for use in Europe, Australia and other 220/240 volt areas of the world.
We normally stock this transformer now. Email me for more information on the 220/240 volt VTA ST-120 amp kit

 


 


21 step attenuator as shown above.
$50 added to ST-120 KIT
$75 added to ST-120 WIRED amp

Time Delay Relay

This is a "time delay relay" board" for tube amps and preamps.
The time delay allows the tube filament heaters to come up before any high voltage is applied. The time delay is nominally about 17 seconds but may be adjusted for more or less delay at the discretion of the user. There are complete instructions for the assembly and installation of the board. In a stock ST-70 the board replaces lugs 5, 6 and 7 of the 7 lug terminal strip. In a VTA ST-70/ST-120 tube amp kit, the VTA-TDB replaces the 3 lug terminal strip. The VTA-TDB may also be easily retrofitted to any VTA ST-70/ST-120 tube amp kit.

The board is 1 7/8 inches wide by 2 1/2 inches long. It takes about 1/2 hour to assemble and is powered by a 6.3 volt AC line taken off V2. When the board is powered up a RED LED lights up to show that the board has power. About 17 seconds after power is applied, a GREEN LED comes on, and the relay kicks in to apply high voltage to your amp. Another nice thing is that if you are in an area that has quick ON/OFF/ON power interruptions the board will automatically reset itself. In other words, if your power goes OFF and then ON again a split second later the board will automatically reset itself and no high voltage will be applied for another 17 seconds.

This is only a delay board - you still need a solid state or tube rectifier to plug into the rectifer socket. If you use a GZ34 tube rectifier IMHO you can get by without it. If you use a solid state rectifier like the Weber WZ68, which only has a 3 to 5 second delay, I think it is helpful. It would also be helpful if you have the quick ON/OFF/ON power interruptions.

This board is to be used ONLY for solid state rectifiers. If used with a TUBE rectifier, the TDR can cause problems with the normal slow warm up of the tube rectifier and may damage a tube rectifier. If you intend to use a TUBE rectifier ONLY with your amp, you do not need the TDR. If you do use a tube rectifier with the TDR, you should BYPASS the TDR. Instructions are included with the TDR on how to bypass the TDR.

This board is a relay switch that will not apply the high voltage power to the amplifier until after the tube filaments are warmed up, the board has a 17 second delay and that can be changed by changing one resistor on the board.

This is a very heavy duty industrial relay used for 270vac 3 phase and rated at 8 amps, with 1500v of isolation between the contacts. Similar delay circuits I evaluated for tube amp use had 240v contacts with 1000v of isolation and were physically larger, this is a great addition to your tube amp. It can run on 6vAC or 12vDC.

ADD a TDR KIT to your kit amp purchase $35
ADD a TDR to your WIRED amp purchase $60
purchase a TDR KIT separately
from my partner Roy $35
(free shipping in USA only)

 


 


Customer Reviews posted on the Internet . . . . . .

Audio Asylum review #1 of the ST-70 kit Audio Asylum review #1 of the ST-120 kit
Audio Asylum review #2 of the ST-70 kit Audio Asylum review #2 of the ST-120 kit
Audio Asylum review #3 of the ST-70 kit Audio Asylum review #3 of the ST-120 kit
Audio Asylum review #4 of the ST-70 kit Audio Asylum review #4 of the ST-120 kit
Audio Asylum review #5 of the ST-70 kit Audio Asylum review #5 of the ST-120 kit
Audio Asylum review #6 of the ST-70 kit (October 2015) Audio Asylum review #6 of the ST-120 kit (Sept 2015)
Audio Asylum review #7 of the ST-120 kit (April 2016)
M125 build by a first time kit builder (June 2011)
M125 completed - review #1 (March 2013)
M125 review by a Newbie (March 2015)

 


here's a link to a partial view of the build manual


 

check out our tube preamps here . . .

 

visit our new "Dynaco Tube Audio Forum"



 

return to VTA home page

 

 

 tubes 4 hifi
 "the path of least resistance is through a vacuum"